Digi International Inc.
11001 Bren Road East
Minnetonka, MN 55343
877 912-3444 or 952 912-3444
http://www.digi.com
XBee®/XBee-PRO® ZB RF Modules
ZigBee RF Modules by Digi International
Models: XBEE2, XBEEPRO2, PRO S2B
Hardware: S2 and S2B
Firmware Versions:
- 20xx - Coordinator - AT/Transparent Operation
- 21xx - Coordinator - API Operation
- 22xx - Router - AT/Transparent Operation
- 23xx - Router - API Operation
- 28xx - End Device - AT/Transparent Operation
- 29xx - End Device - API Operation
DRAFT
90000976_H
7/21/2011
XBee®/XBee‐PRO®ZBRFModules
© 2011 Digi International, Inc. All rights reserved
Nopartofthecontentsofthismanualmaybetransmittedorreproducedinany
formorbyanymeanswithoutthewrittenpermissionofDigiInternational,Inc.
®isaregisteredtrademarkoftheZigBeeAlliance.
ZigBee
XBee®andXBee‐PRO®areregisteredtrademarksofDigiInternational,Inc.
Technical Support: Phone: (866) 765-9885 toll-free U.S.A. & Canada
(801) 765-9885 Worldwide
8:00 am - 5:00 pm [U.S. Mountain Time]
Live Chat: www.digi.com
Online Support: http://www.digi.com/support/eservice/login.jsp
Email: rf-experts@digi.com
©2011DigiInternational,Inc. 2
XBee®/XBee‐PRO®ZBRFModules
Contents
Overview 6
What's New in 2x7x 6
Firmware 6
Manual 7
Key Features 8
Worldwide Acceptance 8
Specifications 9
Hardware Specs for Programmable Variant 10
Mechanical Drawings 10
SIF Header Interface 11
Mounting Considerations 12
Pin Signals 13
EM250 Pin Mappings 14
Design Notes 14
Power Supply Design 14
Recommended Pin Connections 15
Board Layout 15
Electrical Characteristics 17
Module Operation for Programmable Variant 17
XBEE Programmable Bootloader 19
Overview 19
Bootloader Software Specifics 19
Bootloader Menu Commands 24
Firmware Updates 25
Output File configuration 25
RF Module Operation 27
Serial Communications 27
UART Data Flow 27
Serial Buffers 27
Serial Flow Control 28
Serial Interface Protocols 29
Modes of Operation 31
Idle Mode 31
Transmit Mode 31
Receive Mode 32
Command Mode 32
Sleep Mode 33
XBee ZigBee Networks 34
Introduction to ZigBee 34
ZigBee Stack Layers 34
Networking Concepts 34
Device Types 34
PAN ID 35
Operating Channel 36
ZigBee Application Layers: In Depth 36
Application Support Sublayer (APS) 36
Application Profiles 36
Coordinator Operation 37
Forming a Network 37
Channel Selection 37
PAN ID Selection 37
Security Policy 38
Persistent Data 38
XBee ZB Coordinator Startup 38
Permit Joining 39
Resetting the Coordinator 39
Leaving a Network 39
Replacing a Coordinator (Security Disabled Only) 40
Example: Starting a Coordinator 40
Example: Replacing a Coordinator (security disabled) 41
Router Operation 41
Discovering ZigBee Networks 41
Joining a Network 41
Authentication 41
Persistent Data 42
XBee ZB Router Joining 42
Permit Joining 44
Joining Always Enabled 44
Joining Temporarily Enabled 44
Router Network Connectivity 44
Leaving a Network 46
Resetting the Router 47
Example: Joining a Network 47
End Device Operation 47
Discovering ZigBee Networks 47
Joining a Network 48
Parent Child Relationship 48
End Device Capacity 48
Authentication 48
Persistent Data 48
Orphan Scans 48
XBee: ZB End Device Joining 49
Parent Connectivity 50
Resetting the End Device 50
Leaving a Network 50
Example: Joining a Network 50
Channel Scanning 51
©2011DigiInternaitonal,Inc. 3
XBee®/XBee‐PRO®ZBRFModules
Contents
Managing Multiple ZigBee Networks 51
PAN ID Filtering 51
Preconfigured Security Keys 51
Permit Joining 52
Application Messaging 52
Transmission, Addressing, and Routing 53
Addressing 53
64-bit Device Addresses 53
16-bit Device Addresses 53
Application Layer Addressing 53
Data Transmission 53
Broadcast Transmissions 54
Unicast Transmissions 54
Data Transmission Examples 56
RF Packet Routing 57
Link Status Transmission 58
AODV Mesh Routing 59
Many-to-One Routing 61
Source Routing 61
Encrypted Transmissions 64
Maximum RF Payload Size 64
Throughput 65
ZDO Transmissions 65
ZigBee Device Objects (ZDO) 65
Sending a ZDO Command 66
Receiving ZDO Commands and Responses 66
Transmission Timeouts 67
Unicast Timeout 68
Extended Timeout 68
Transmission Examples 69
Security 71
Security Modes 71
ZigBee Security Model 71
Network Layer Security 71
Frame Counter 72
Message Integrity Code 72
Network Layer Encryption and Decryption 72
Network Key Updates 72
APS Layer Security 72
Message integrity Code 73
APS Link Keys 73
APS Layer Encryption and Decryption 73
Network and APS Layer Encryption 73
Trust Center 74
Forming and Joining a Secure Network 74
Implementing Security on the XBee 74
Enabling Security 75
Setting the Network Security Key 75
Setting the APS Trust Center Link Key 75
Enabling APS Encryption 75
Using a Trust Center 75
XBee Security Examples 76
Example 1: Forming a network with security (pre-configured link keys) 76
Example 2: Forming a network with security (obtaining keys during joining) 76
Network Commissioning and Diagnostics 78
Device Configuration 78
Device Placement 78
Link Testing 78
RSSI Indicators 79
Device Discovery 79
Network Discovery 79
ZDO Discovery 79
Joining Announce 79
Commissioning Pushbutton and Associate LED 79
Commissioning Pushbutton 80
Associate LED 81
Managing End Devices 83
End Device Operation 83
Parent Operation 83
End Device Poll Timeouts 84
Packet Buffer Usage 84
Non-Parent Device Operation 84
XBee End Device Configuration 85
Pin Sleep 85
Cyclic Sleep 87
Transmitting RF Data 90
Receiving RF Data 90
IO Sampling 91
Waking End Devices with the Commissioning Pushbutton 91
Parent Verification 91
Rejoining 91
XBee Router/Coordinator Configuration 91
RF Packet Buffering Timeout 92
Child Poll Timeout 92
©2011DigiInternaitonal,Inc. 4
XBee®/XBee‐PRO®ZBRFModules
Contents
Transmission Timeout 92
Putting it all Together 93
Short Sleep Periods 93
Extended Sleep Periods 93
Sleep Examples 93
XBee Analog and Digital IO Lines 95
IO Configuration 95
IO Sampling 95
Queried Sampling 97
Periodic IO Sampling 97
Change Detection Sampling 97
RSSI PWM 97
IO Examples 98
API Operation 99
API Frame Specifications 99
API Examples 101
API UART Exchanges 102
AT Commands 102
Transmitting and Receiving RF Data 102
Remote AT Commands 102
Source Routing 103
Supporting the API 103
API Frames 103
AT Command 103
AT Command - Queue Parameter Value 104
ZigBee Transmit Request 104
Explicit Addressing ZigBee Command Frame 106
Remote AT Command Request 108
Create Source Route 109
AT Command Response 110
Modem Status 110
ZigBee Transmit Status 111
ZigBee Receive Packet 112
ZigBee Explicit Rx Indicator 113
ZigBee IO Data Sample Rx Indicator 114
XBee Sensor Read Indicator 115
Node Identification Indicator 117
Remote Command Response 118
Over-the-Air Firmware Update Status 119
Route Record Indicator 120
Many-to-One Route Request Indicator 121
Sending ZigBee Device Objects (ZDO) Commands
with the API 122
Sending ZigBee Cluster Library (ZCL) Commands
with the API 124
Sending Public Profile Commands with the API 126
XBee Command Reference Tables 129
Module Support 139
X-CTU Configuration Tool 139
Customizing XBee ZB Firmware 139
Design Considerations for Digi Drop-In Networking
139
XBee Bootloader 139
Programming XBee Modules 140
Serial Firmware Updates 140
Invoke XBee Bootloader 140
Send Firmware Image 140
SIF Firmware Updates 141
Writing Custom Firmware 141
Regulatory Compliance 141
Enabling GPIO 1 and 2 141
Detecting XBee vs. XBee-PRO 142
Ensuring Optimal Output Power 142
Improving Low Power Current Consumption 143
XBee (non-PRO) Initialization: 143
When sleeping (end devices): 143
When waking from sleep (end devices): 143
Appendix A:Definitions 144
Appendix B: Agency Certifications 146
Appendix C:Migrating from ZNet 2.5 to XBee ZB 154
Appendix D:Additional Information 155
©2011DigiInternaitonal,Inc. 5
1.Overview
This manual describes the operation of the XBee/XBee-PRO ZB RF module, which
consists of ZigBee firmware loaded onto XBee S2 and S2B hardware, models:
XBEE2, XBEEPRO2 and PRO S2B. The XBee/XBee-PRO ZB RF Modules are
designed to operate within the ZigBee protocol and support the unique needs of
low-cost, low-power wireless sensor networks. The modules require minimal
power and provide reliable delivery of data between remote devices.
The modules operate within the ISM 2.4 GHz frequency band and are compatible
with the following:
•XBee RS-232 Adapter
•XBee RS-485 Adapter
•XBee Analog I/O Adapter
•XBee Digital I/O Adapter
•XBee Sensor
•XBee USB Adapter
•XStick
•ConnectPort X Gateways
•XBee Wall Router.
The XBee/XBee-PRO ZB firmware release can be installed on XBee ZNet or ZB modules. The XBee ZB firmware is based
on the EmberZNet 3.x ZigBee PRO Feature Set mesh networking stack, while the XBee ZNet 2.5 firmware is based on
Ember's proprietary "designed for ZigBee" mesh stack (EmberZNet 2.5.x). ZB and ZNet 2.5 firmware are similar in
nature, but not over-the-air compatible. Devices running ZNet 2.5 firmware cannot talk to devices running the ZB firmware.
What's New in 2x7x
Firmware
XBee/XBee-PRO ZB firmware includes the following new features (compared with 2x6x):
•Using Ember stack version 3.4.1.
•Support for the PRO S2B with temperature compensation and an overvoltage check. Within 15 seconds of
the supply voltage exceeding 3.9V, the API will emit a 0x08 modem status (Overvoltage) message, and
then the AT/API versions will do a watchdog reset.
•ZDO pass-through added. If AO=3, then ZDO requests which are not supported by the stack will be
passed out the UART.
•An attempt to send an oversized packet (256+ bytes) will result in a Tx Status message with a status code
of 0x74.
•End devices have two speed polling. 7.5 seconds is the slow rate, which switches to the fast rate to transact with its parent. When transactions are done, it switches back to the slow rate.
•A new receive option bit (0x40) indicates if the packet came from an end device.
•Added extended timeout option since end devices need more time than routers to ack their packets.
•An option bit (0x01) was added to disable APS retries.
•If an end device has not had its polls answered for 5 secs, it will leave and attempt to rejoin the network.
•XBee S2B has a new TP command which returns the temperature compensation sensor reading in units of
Celsius degrees.
•The PP command returns the power dBm setting when PL4 is selected.
•The PO command sets the slow polling rate on end devices. Range is 1-0x1770 in units of 10 msec (10
msec to 60 sec). Default is 0 which invokes a 100 msec delay.
•Rejoining now can proceed without a NR or NRO command after a Mgmt_Leave_req is processed.
•Command ranges were changed for the SC, IR, and LT commands.
•A PAN ID corruption problem was fixed.
See the 2x7x release notes for a complete list of new features and bug fixes at www.digi.com/support.
©2011DigiInternational,Inc. 6
XBee®/XBee‐PRO®ZBRFModules
Manual
The XBee/XBee-PRO/S2B ZB 2x7x manual includes the following corrections over the 2x6x manual:
•Descriptions and specification for the PRO S2B.
•SIF Header Interface, pin 8 relabeled as pin 10.
•Pin mappings for pins 22 and 24 updated.
•New modem status codes were added.
•Corrections to the ZigBee Receive Packet description.
•Description changes for the SC, PL, PP, AO, IR, %V, and PO commands.
•Updates to Appendix B.
©2011DigiInternational,Inc. 7
XBee®/XBee‐PRO®ZBRFModules
High Performance, Low Cost
XBee
• Indoor/Urban: up to 133’ (40 m)
• Outdoor line-of-sight: up to 400’ (120 m)
• Transmit Power: 2 mW (3 dBm)
• Receiver Sensitivity: -96 dBm
XBee-PRO (S2)
• Indoor/Urban: up to 300’ (90 m), 200' (60
m) for International variant
• Outdoor line-of-sight: up to 2 miles (3200
m), 5000' (1500 m) for International variant
• Transmit Power: 50mW (17dBm), 10mW
(10dBm) for International variant
• Receiver Sensitivity: -102 dBm
XBee-PRO (S2B)
• Indoor/Urban: up to 300’ (90 m), 200' (60
m) for International variant
• Outdoor line-of-sight: up to 2 miles (3200
m), 5000' (1500 m) for International variant
• Transmit Power: 63mW (18dBm), 10mW
(10dBm) for International variant
• Receiver Sensitivity: -102 dBm
Advanced Networking & Security
Retries and Acknowledgements
DSSS (Direct Sequence Spread Spectrum)
Each direct sequence channel has over
65,000 unique network addresses available
Point-to-point, point-to-multipoint
and peer-to-peer topologies supported
Self-routing, self-healing and fault-tolerant
mesh networking
Low Power
XBee
• TX Peak Current: 40 mA (@3.3 V)
• RX Current: 40 mA (@3.3 V)
• Power-down Current: < 1 A
XBee-PRO (S2)
• TX Peak Current: 295mA (170mA for
international variant)
• RX Current: 45 mA (@3.3 V)
• Power-down Current: 3.5 A typical
@ 25 degrees C
XBee-PRO (S2B)
• TX Peak Current: 205mA (117mA for
international variant)
• RX Current: 47 mA (@3.3 V)
• Power-down Current: 3.5 A typical
@ 25 degrees C
Easy-to-Use
No configuration necessary for out-of box
RF communications
AT and API Command Modes for
configuring module parameters
Small form factor
Extensive command set
Free X-CTU Software
(Testing and configuration software)
Free & Unlimited Technical Support
Key Features
©2011DigiInternational,Inc. 8
Worldwide Acceptance
FCC Approval (USA) Refer to Appendix A for FCC Requirements. Systems that contain XBee®/
XBee-PRO® ZB RF Modules inherit Digi Certifications.
ISM (Industrial, Scientific & Medical) 2.4 GHz frequency band
Manufactured under ISO 9001:2000 registered standards
XBee®/XBee-PRO® ZB RF Modules are optimized for use in US, Canada, Europe, Australia, and
Japan (contact Digi for complete list of agency approvals).
XBee®/XBee‐PRO®ZBRFModules
Specifications
SpecificationsoftheXBee®/XBee‐PRO®ZBRFModule
Specification XBee XBee-PRO (S2) XBee-PRO (S2B)
Performance
Indoor/Urban Range up to 133 ft. (40 m)
Outdoor RF line-of-sight
Range
Transmit Power Output
RF Data Rate 250,000 bps 250,000 bps 250,000 bps
Data Throughput up to 35000 bps (see chapter 4) up to 35000 bps (see chapter 4) up to 35000 bps (see chapter 4)
Serial Interface Data Rate
(software selectable)
Receiver Sensitivity
Power Requirements
Supply Voltage 2.1 - 3.6 V 3.0 - 3.4 V 2.7 - 3.6 V
Operating Current
(Transmit, max output
power)
Operating Current
(Receive))
Idle Current (Receiver off) 15mA 15mA 15mA
Power-down Current
General
Operating Frequency
Band
Dimensions 0.960” x 1.087” (2.438cm x 2.761cm) 0.960 x 1.297 (2.438cm x 3.294cm) 0.960 x 1.297 (2.438cm x 3.294cm)
Operating Temperature -40 to 85º C (industrial) -40 to 85º C (industrial) -40 to 85º C (industrial)
Antenna Options
Networking & Security
Supported Network
Topologies
Number of Channels 16 Direct Sequence Channels 14 Direct Sequence Channels 15 Direct Sequence Channels
Channels 11 to 26 11 to 24 11 to 25
Addressing Options
Agency Approvals
United States (FCC Part
15.247)
Industry Canada (IC) IC: 4214A-XBEE2 IC: 1846A-XBEEPRO2 IC: 1846A-PROS2B
Europe (CE) ETSI ETSI (International variant) ETSI (10 mW max)
Up to 300 ft. (90 m), up to 200 ft (60 m)
international variant
up to 400 ft. (120 m)
2mW (+3dBm), boost mode enabled
1.25mW (+1dBm), boost mode
disabled
1200 bps - 1 Mbps
(non-standard baud rates also
supported)
-96 dBm, boost mode enabled
-95 dBm, boost mode disabled
40mA (@ 3.3 V, boost mode
enabled)
35mA (@ 3.3 V, boost mode
disabled)
40mA (@ 3.3 V, boost mode
enabled)
38mA (@ 3.3 V, boost mode
disabled)
o
< 1 uA @ 25
ISM 2.4 GHz ISM 2.4 GHz ISM 2.4 GHz
Integrated Whip, Chip, RPSMA, or
U.FL Connector
Point-to-point, Point-to-multipoint,
Peer-to-peer, and Mesh
PAN ID and Addresses, Cluster IDs
and Endpoints (optional)
FCC ID: OUR-XBEE2 FCC ID: MCQ-XBEEPRO2 FCC ID: MCQ-PROS2B
C3.5 A typical @ 25oC3.5 A typical @ 25oC
Up to 2 miles (3200 m), up to 5000 ft
(1500 m) international variant
50mW (+17 dBm)
10mW (+10 dBm) for International
variant
1200 bps - 1 Mbps
(non-standard baud rates also
supported)
-102 dBm -102 dBm
295mA (@3.3 V)
170mA (@3.3 V) international variant
45 mA (@3.3 V)
Integrated Whip Antenna, Embedded
PCB Antenna, RPSMA or U.FL
Connector
Point-to-point, Point-to-multipoint, Peerto-peer, and Mesh
PAN ID and Addresses, Cluster IDs and
Endpoints (optional)
Up to 300 ft. (90 m), up to 200 ft (60 m)
international variant
Up to 2 miles (3200 m), up to 5000 ft (1500
m) international variant
63mW (+18 dBm)
10mW (+10 dBm) for International variant
1200 bps - 1 Mbps
(non-standard baud rates also supported)
205mA, up to 220 mA with programmable
variant (@3.3 V)
117mA, up to 132 mA with programmable
variant (@3.3 V), International variant
47 mA, up to 62 mA with programmable
variant (@3.3 V)
Integrated Whip Antenna, Embedded PCB
Antenna, RPSMA or U.FL Connector
Point-to-point, Point-to-multipoint, Peer-topeer, and Mesh
PAN ID and Addresses, Cluster IDs and
Endpoints (optional)
©2011DigiInternational,Inc. 9
XBee®/XBee‐PRO®ZBRFModules
SpecificationsoftheXBee®/XBee‐PRO®ZBRFModule
Specification XBee XBee-PRO (S2) XBee-PRO (S2B)
Australia C-Tick C-Tick C-Tick
Japan R201WW07215215
RoHS Compliant Compliant Compliant
R201WW08215142 (international
variant)
Hardware Specs for Programmable Variant
The following specifications need to be added to the current measurement of the previous table if the module
has the programmable secondary processor. For example, if the secondary processor is running and
constantly collecting DIO samples at a rate while having the RF portion of the XBEE sleeping the new current
will be I
of the RF portion of the module of the XBEE-PRO (S2B) listed in the table below.
= Ir2 + I0, where I
total
Specificationsoftheprogrammablesecondaryprocessor
Optional Secondary Processor Specification
Runtime current for 32k running at 20MHz +14mA
Runtime current for 32k running at 1MHz +1mA
For additional specifications see Freescale Datasheet and
Minimum Reset low pulse time for EM250 +50 nS (additional resistor increases minimum time)
is the runtime current of the secondary processor and Is is the sleep current
r2
Sleep current +0.5uA typical
Manual
VREF Range 1.8VDC to VCC
R201WW10215062 (international variant)
These numbers add to S2B specifications
(Add to RX, TX, and sleep currents depending on
mode of operation)
MC9SO8QE32
Mechanical Drawings
MechanicaldrawingsoftheXBee®/XBee‐PRO®ZBRFModules(antennaoptionsnotshown)
.
©2011DigiInternational,Inc. 10
XBee®/XBee‐PRO®ZBRFModules
MechanicalDrawingsfortheRPSMAVari a nt
SIF Header Interface
The XBee/XBee-PRO ZB modules include a SIF programming header that can be used with Ember's
programming tools to upload custom firmware images onto the XBee module. The SIF header orientation and
pinout are shown below.
A male header can be populated on the XBee that mates with Ember's 2x5 ribbon cable. The male header and
ribbon cables are available from Samtec:
2x5 Male Header - FTSH-105-01-F-DV-K
2x5 Ribbon Cable - FFSD-05-D-12.00-01-N
©2011DigiInternational,Inc. 11
XBee®/XBee‐PRO®ZBRFModules
Mounting Considerations
The XBee module was designed to mount into a receptacle (socket) and therefore does not require any
soldering when mounting it to a board. The XBee-PRO Development Kits contain RS-232 and USB interface
boards which use two 20-pin receptacles to receive modules.
XBee‐PROModuleMountingtoanRS‐232InterfaceBoard.
The receptacles used on Digi development boards are manufactured by Century Interconnect. Several other
manufacturers provide comparable mounting solutions; however, Digi currently uses the following
receptacles:
• Through-hole single-row receptacles -
Samtec P/N: MMS-110-01-L-SV (or equivalent)
• Through-hole single-row receptacles -
Mill-Max P/N: 831-43-0101-10-001000
• Surface-mount double-row receptacles -
Century Interconnect P/N: CPRMSL20-D-0-1 (or equivalent)
• Surface-mount single-row receptacles -
Samtec P/N: SMM-110-02-SM-S
Digi also recommends printing an outline of the module on the board to indicate the orientation the
module should be mounted.
©2011DigiInternational,Inc. 12
XBee®/XBee‐PRO®ZBRFModules
Pin Signals
PinAssignmentsfortheXBee/XBee‐PROModules
Pin # Name Direction Default State Description
1 VCC - - Power supply
2 DOUT Output Output UART Data Out
3 DIN / CONFIG
4 DIO12 Both Disabled Digital I/O 12
5 RESET
6 RSSI PWM / DIO10 Both Output RX Signal Strength Indicator / Digital IO
7 DIO11 Both Input Digital I/O 11
8 [reserved] - Disabled Do not connect
9DTR
10 GND - - Ground
11 DIO4 Both Disabled Digital I/O 4
12 CTS
13 ON / SLEEP
14 VREF Input -
15 Associate / DIO5 Both Output Associated Indicator, Digital I/O 5
16 RTS
17 AD3 / DIO3 Both Disabled Analog Input 3 or Digital I/O 3
18 AD2 / DIO2 Both Disabled Analog Input 2 or Digital I/O 2
19 AD1 / DIO1 Both Disabled Analog Input 1 or Digital I/O 1
20
(Low‐assertedsignalsaredistinguishedwithahorizontallineabovesignalname.)
Input Input UART Data In
Both
/ SLEEP_RQ/ DIO8 Both Input Pin Sleep Control Line or Digital IO 8
/ DIO7 Both Output
Output Output Module Status Indicator or Digital I/O 9
/ DIO6 Both Input
AD0 / DIO0 /
Commissioning Button
Both Disabled
Open-Collector with
pull-up
Module Reset (reset pulse must be at least 200
ns)
Clear-to-Send Flow Control or Digital I/O 7. CTS, if
enabled, is an output.
Not used for EM250. Used for programmable
secondary processor.
For compatibility with other XBEE modules, we
recommend connecting this pin voltage reference
if Analog sampling is desired.
Otherwise, connect to GND.
Request-to-Send Flow Control, Digital I/O 6. RTS,
if enabled, is an input.
Analog Input 0, Digital IO 0, or Commissioning
Button
• Signal Direction is specified with respect to the module
• See Design Notes section below for details on pin connections.
©2011DigiInternational,Inc. 13
XBee®/XBee‐PRO®ZBRFModules
EM250 Pin Mappings
The following table shows how the EM250 pins are used on the XBee.
EM250 Pin Number XBee Pin Number Other Usage
13 (Reset) 5* Connected to pin 8 on 2x5 SIF header.
19 (GPIO 11) 16*
20 (GPIO 12) 12*
21 (GPIO 0)
22 (GPIO 1)
24 (GPIO 2)
25 (GPIO 3) 13
26 (GPIO 4 / ADC 0) 20 Connected to pin 9 on 2x5 SIF header.
27 (GPIO 5 / ADC 1) 19 Connected to pin 10 on 2x5 SIF header.
29 (GPIO 6 /ADC 2) 18
30 (GPIO 7 / ADC 3 17
31 (GPIO 8) 4
32 (GPIO 9) 2*
33 (GPIO 10) 3*
34 (SIF_CLK) Connected to pin 6 on 2x5 SIF header.
35 (SIF_MISO) Connected to pin 2 on 2x5 SIF header.
36 (SIF_MOSI) Connected to pin 4 on 2x5 SIF header.
37 (SIF_LOAD) Connected to pin 7 on 2x5 SIF header.
40 (GPIO 16) 7
41 (GPIO 15) 6
42 (GPIO 14) 9
43 (GPIO 13) 11
15
XBee
Tied to ground (module identification)
XBee-PRO (S2)
Low-asserting shutdown line for output power compensation circuitry.
XBee-PRO (S2B)
Used to communicate with Temp Sensor and control Shutdown for low power mode.
XBee
Not connected. Configured as output low.
XBee-PRO (S2)
Powers the output power compensation circuitry.
XBee-PRO (S2B)
Used to communicate with Temp Sensor and control Shutdown for low power mode.
* NOTE: These lines may not go to the external XBEE pins of the module if the programmable secondary processor
is populated.
Design Notes
The XBee modules do not specifically require any external circuitry or specific connections for proper
operation. However, there are some general design guidelines that are recommended for help in
troubleshooting and building a robust design.
Power Supply Design
Poor power supply can lead to poor radio performance especially if the supply voltage is not kept within
tolerance or is excessively noisy. To help reduce noise a 1uF and 8.2pF capacitor are recommended to be
placed as near to pin1 on the PCB as possible. If using a switching regulator for your power supply, switching
frequencies above 500kHz are preferred. Power supply ripple should be limited to a maximum 250mV peak to
peak.
Note – For designs using the programmable modules an additional 10uF decoupling cap is recommended near
pin 1 of the module. The nearest proximity to pin 1 of the 3 caps should be in the following order: 8.2pf, 1uF
followed by 10uF.
©2011DigiInternational,Inc. 14
XBee®/XBee‐PRO®ZBRFModules
Recommended Pin Connections
The only required pin connections are VCC, GND, DOUT and DIN. To support serial firmware updates, VCC,
GND, DOUT, DIN, RTS, and DTR should be connected.
All unused pins should be left disconnected. All inputs on the radio can be pulled high with 30k internal pull-up
resistors using the PR software command. No specific treatment is needed for unused outputs.
For applications that need to ensure the lowest sleep current, inputs should never be left floating. Use internal
or external pull-up or pull-down resistors, or set the unused I/O lines to outputs.
Other pins may be connected to external circuitry for convenience of operation including the Associate LED pin
(pin 15) and the Commissioning pin (pin 20). The Associate LED pin will flash differently depending on the
state of the module to the network, and a pushbutton attached to pin 20 can enable various join functions
without having to send UART commands. Please see the commissioning pushbutton and associate LED section
in chapter 7 for more details. The source and sink capabilities are limited to 4mA for all pins on the module.
The VRef pin (pin 14) is not used on this module. For compatibility with other XBee modules, we recommend
connecting this pin to a voltage reference if analog sampling is desired. Otherwise, connect to GND.
Board Layout
XBee modules do not have any specific sensitivity to nearby processors, crystals or other PCB components.
Other than mechanical considerations, no special PCB placement is required for integrating XBee radios except
for those with integral antennas. In general, Power and GND traces should be thicker than signal traces and be
able to comfortably support the maximum currents.
The radios are also designed to be self sufficient and work with the integrated and external antennas without
the need for additional ground planes on the host PCB. However, considerations should be taken on the choice
of antenna and antenna location. Metal objects that are near an antenna cause reflections and may reduce the
ability for an antenna to efficiently radiate. Using an integral antenna (like a wire whip antenna) in an enclosed
metal box will greatly reduce the range of a radio. For this type of application an external antenna would be a
better choice.
External antennas should be positioned away from metal objects as much as possible. Metal objects next to
the antenna or between transmitting and receiving antennas can often block or reduce the transmission
distance. Some objects that are often overlooked are metal poles, metal studs or beams in structures,
concrete (it is usually reinforced with metal rods), metal enclosures, vehicles, elevators, ventilation ducts,
refrigerators and microwave ovens.
The Wire Whip Antenna should be straight and perpendicular to the ground plane and/or chassis. It should
reside above or away from any metal objects like batteries, tall electrolytic capacitors or metal enclosures. If
the antenna is bent to fit into a tight space, it should be bent so that as much of the antenna as possible is
away from metal. Caution should be used when bending the antenna, since this will weaken the solder joint
where the antenna connects to the module. Antenna elements radiate perpendicular to the direction they
point. Thus a vertical antenna emits across the horizon.
Embedded PCB or Chip Antennas should not have any ground planes or metal objects above or below the
module at the antenna location. For best results the module should be in a plastic enclosure, instead of metal
one. It should be placed at the edge of the PCB to which it is mounted. The ground, power and signal planes
should be vacant immediately below the antenna section (See drawing for recommended keepout area).
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XBee®/XBee‐PRO®ZBRFModules
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XBee®/XBee‐PRO®ZBRFModules
Electrical Characteristics
DCCharacteristicsoftheXBee/XBee‐PRO
Symbol Parameter Condition Min Typical Max Units
V
IL
V
IH
V
OL
V
OH
I
IIN
I
OHS
I
OHH
I
OLS
I
OLH
I
OH + IOL
V
REFI
V
IADC
R
IS
R
I
Note – The signal-ended ADC measurements are limited in their range and only guaranteed for accuracy in
the range 0 to VREFI. The nature of the ADC’s internal design allows for measurements outside of this range
(+/- 200mV), but the accuracy of such measurements are not guaranteed.
Input Low Voltage All Digital Inputs - - 0.2 * VCC V
Input High Voltage All Digital Inputs 0.8 * VCC - - V
Output Low Voltage VCC >= 2.7 V - - 0.18*VCC V
Output High Voltage VCC >= 2.7 V 0.82*VCC - - V
Input Leakage Current
Output source current (standard)
Output source current (high
current)
Output sink current (standard
Output sink current (high current) RSSI/PWM, DIO10, DIO4 digital outputs 8 mA
Total output current for all I/O pins All digital outputs 40 mA
VREF Internal
ADC input voltage range 0 VREFI V
Input impedance When taking a sample 1 M Ohm
Input Impedance When not taking a sample 10 M Ohm
= VCC or GND, all inputs, per pin
V
IN
All digital outputs except
RSSI/PWM, DIO10, DIO4
- - 0.5uA uA
4mA
RSSI/PWM, DIO10, DIO4 digital outputs 8 mA
All digital inputs except
RSSI/PWM, DIO10, DIO4
EM250 has an internal reference that is
fixed
1.19 1.2 1.21 V
4mA
Module Operation for Programmable Variant
The S2B modules that have the programmable option populated have a secondary processor with 32k of flash
and 2k of RAM. This allows module integrators to put custom code on the XBEE module to fit their own unique
needs. The DIN, DOUT, RTS, CTS, and RESET lines are intercepted by the secondary processor to allow it to be
in control of the data transmitted and received. All other lines are in parallel and can be controlled by either
the EM250 or the MC9S08QE micro (see Block Diagram for details). The EM250 by default has control of
certain lines. These lines can be released by the EM250 by sending the proper command(s) to disable the
desired DIO line(s) (see XBEE Command Reference Tables).
In order for the secondary processor to sample with ADCs, the XBEE pin 14 (VREF) needs to be connected to
a reference voltage.
Digi provides a bootloader that can take care of programming the processor over the air or through the serial
interface. This means that over the air updates can be supported through an XMODEM protocol. The processor
can also be programmed and debugged through a one wire interface BKGD (Pin 8).
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XBee®/XBee‐PRO®ZBRFModules
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XBee®/XBee‐PRO®ZBRFModules
XBEE Programmable Bootloader
Overview
The Xbee Programmable module is equipped with a Freescale MC9S08QExx application processor. This
application processor comes with a supplied bootloader. The following section describes how to interface the
customer's application code running on this processor to the XBee Programmable module's supplied
bootloader.
This section discusses how to initiate firmware updates using the supplied bootloader for wired and over-theair updates.
Bootloader Software Specifics
Memory Layout
Figure 1 shows the memory map for the MC9S08QE32 application processor.
The supplied bootloader occupies the bottom pages of the flash from 0xF200 to 0xFFFF. Application
code cannot write to this space.
The application code can exist in Flash from address 0x8400 to 0xF1BC. 1k of Flash from 0x8000 to
0x83FF is reserved for Non Volatile Application Data that will not be erased by the bootloader during a
flash update.
A portion of RAM is accessible by both the application and the bootloader. Specifically, there is a
shared data region used by both the application and the bootloader that is located at RAM address
0x200 to 0x215. Application code should not write anything to AppResetCause or BLResetCause unless
informing the bootloader of the impending reset reason.
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XBee®/XBee‐PRO®ZBRFModules
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XBee®/XBee‐PRO®ZBRFModules
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XBee®/XBee‐PRO®ZBRFModules
Operation
Upon reset of any kind, the execution control begins with the bootloader.
If the reset cause is Power-On reset (POR), Pin reset (PIN), or Low Voltage Detect(LVD) reset the
bootloader will not jump to the application code if the override bits are set to RTS(D7)=1, DTR(D5)=0,
and DIN(B0)=0. Otherwise, the bootloader writes the reset cause "NOTHING" to the shared data
region, and jumps to the Application.
Reset causes are defined in the file common. h in an enumeration with the following definitions:
typedef enum {
BL_CAUSE_NOTHING = 0x0000, //PIN, LVD, POR
BL_CAUSE_NOTHING_COUNT = 0x0001,//BL_Reset_Cause counter
// Bootloader increments cause every reset
BL_CAUSE_BAD_APP = 0x0010,//Bootloader considers APP invalid
} BL_RESET_CAUSES;
typedef enum {
APP_CAUSE_NOTHING = 0x0000,
APP_CAUSE_USE001 = 0x0001,
// 0x0000 to 0x00FF are considered valid for APP use.
APP_CAUSE_USE255 = 0x00FF,
APP_CAUSE_FIRMWARE_UPDATE = 0x5981,
APP_CAUSE_BYPASS_MODE = 0x4682,
APP_CAUSE_BOOTLOADER_MENU = 0x6A18,
} APP_RESET_CAUSES;
Otherwise, if the reset cause is a "watchdog" or other reset, the bootloader checks the shared memory
region for the APP_RESET_CAUSE. If the reset cause is:
1."APP_CAUSE_NOTHING" or 0x0000 to 0x00FF, the bootloader increments the
BL_RESET_CAUSES, verifies that it is still less than BL_CAUSE_BAD_APP, and jumps back to
the application. If the Application does not clear the BL_RESET_CAUSE, it can prevent an
infinite loop of running a bad application that continues to perform illegal instructions or
watchdog resets.
2."APP_CAUSE_FIRMWARE_UPDATE", the bootloader has been instructed to update the
application "over-the-air" from a specific 64 bit address. In this case, the bootloader will
attempt to initiate an Xmodem transfer from the 64 bit address located in Shared RAM.
3."APP_CAUSE_BYPASS_MODE", the bootloader executes bypass mode. This mode passes the
local UART data directly to the EM250 allowing for direct communication with the EM250.
The only way to exit bypass mode is to reset or power cycle the module.
If none of the above is true, the bootloader will enter "Command mode". In this mode, users can
initiate firmware downloads both wired and over-the-air, check application/bootloader version strings,
and enter Bypass mode.
Application version string
Figure 1 shows an "Application version string pointer" area in application flash which holds the pointer
to where the application version string resides. The application's linker command file ultimately
determines where this string is placed in application flash.
It is preferable that the application version string be located at address 0x8400 for MC9S08QE32 parts.
The application string can be any characters terminated by the NULL character (0x00). There is not a
strict limit on the number of characters in the string, but for practical purposes should be kept under
100 bytes including the terminating NULL character. During an update the bootloader erases the entire
application from 0x8400 on. The last page has the vector table specifically the redirected reset vector.
The version string pointer and reset vector are used to determine if the application is valid.
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XBee®/XBee‐PRO®ZBRFModules
Application Interrupt Vector table and Linker Command File
Since the bootloader flash region is read-only, the interrupt vector table is redirected to the region
0xF1C0 to 0xF1FD so that application developers can use hardware interrupts. Note that in order for
Application interrupts to function properly, the Application's linker command file (*.prm extension)
must be modified appropriately to allow the linker to place the developers code in the correct place in
memory. For example, the developer desires to use the serial communications port SCI1 receive
interrupt. The developer would add the following line to the Codewarrior linker command file for the
project…
VECTOR ADDRESS 0x0000F1E0 vSci1Rx
This will inform the linker that the interrupt function "vSci1Rx()" should be placed at address
0x0000F1E0. Next, the developer should add a file to their project "vector_table.c" that creates an
array of function pointers to the ISR routines used by the application…Eg.
extern void _Startup(void);/* _Startup located in Start08.c */
extern void vSci1Rx(void);/* sci1 rx isr */
extern short iWriteToSci1(unsigned char *);
void vDummyIsr(void);
#pragma CONST_SEG VECTORS
void (* const vector_table[])(void) = /* Relocated Interrupt vector table */{
vDummyIsr,/* Int.no. 0 Vtpm3ovf (at F1C0)Unassigned */
vDummyIsr, /* Int.no. 1 Vtpm3ch5 (at F1C2) Unassigned */
vDummyIsr, /* Int.no. 2 Vtpm3ch4 (at F1C4) Unassigned */
vDummyIsr, /* Int.no. 3 Vtpm3ch3 (at F1C6) Unassigned */
vDummyIsr, /* Int.no. 4 Vtpm3ch2 (at F1C8) Unassigned */
vDummyIsr, /* Int.no. 5 Vtpm3ch1 (at F1CA) Unassigned */
vDummyIsr, /* Int.no. 6 Vtpm3ch0 (at F1CC) Unassigned */
vDummyIsr, /* Int.no. 7 Vrtc (at F1CE) Unassigned */
vDummyIsr, /* Int.no. 8 Vsci2tx (at F1D0) Unassigned */
vDummyIsr, /* Int.no. 9 Vsci2rx (at F1D2) Unassigned */
vDummyIsr, /* Int.no. 10 Vsci2err (at F1D4) Unassigned */
vDummyIsr, /* Int.no. 11 Vacmpx (at F1D6) Unassigned */
vDummyIsr, /* Int.no. 12 Vadc (at F1D8) Unassigned */
vDummyIsr, /* Int.no. 13 Vkeyboard (at F1DA) Unassigned */
vDummyIsr, /* Int.no. 14 Viic (at F1DC) Unassigned */
vDummyIsr, /* Int.no. 15 Vsci1tx (at F1DE) Unassigned */
vSci1Rx, /* Int.no. 16 Vsci1rx (at F1E0) SCI1RX */
vDummyIsr, /* Int.no. 17 Vsci1err (at F1E2) Unassigned */
vDummyIsr, /* Int.no. 18 Vspi (at F1E4) Unassigned */
vDummyIsr, /* Int.no. 19 VReserved12 (at F1E6) Unassigned */
vDummyIsr, /* Int.no. 20 Vtpm2ovf (at F1E8) Unassigned */
vDummyIsr, /* Int.no. 21 Vtpm2ch2 (at F1EA) Unassigned */
vDummyIsr, /* Int.no. 22 Vtpm2ch1 (at F1EC) Unassigned */
vDummyIsr, /* Int.no. 23 Vtpm2ch0 (at F1EE) Unassigned */
vDummyIsr, /* Int.no. 24 Vtpm1ovf (at F1F0) Unassigned */
vDummyIsr, /* Int.no. 25 Vtpm1ch2 (at F1F2) Unassigned */
vDummyIsr, /* Int.no. 26 Vtpm1ch1 (at F1F4) Unassigned */
vDummyIsr, /* Int.no. 27 Vtpm1ch0 (at F1F6) Unassigned */
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XBee®/XBee‐PRO®ZBRFModules
};
void vDummyIsr(void){
for(;;){
if(iWriteToSci1("STUCK IN UNASSIGNED ISR\n\r>"));
}
}
The interrupt routines themselves can be defined in separate files. The "vDummyIsr" function is used
in conjunction with "iWritetoSci1" for debugging purposes.
Bootloader Menu Commands
The bootloader accepts commands from both the local UART and OTA. All OTA commands sent must be
Unicast with only 1 byte in the payload for each command. A response will be returned to the sender. All
Broadcast and multiple byte OTA packets are dropped to help prevent general OTA traffic from being
interpreted as a command to the bootloader while in the menu.
Bypass Mode - "B"
vDummyIsr, /* Int.no. 28 Vlvd (at F1F8) Unassigned */
vDummyIsr, /* Int.no. 29 Virq (at F1FA) Unassigned */
vDummyIsr, /* Int.no. 30 Vswi (at F1FC) Unassigned */
_Startup /* Int.no. 31 Vreset (at F1FE) Reset vector */
The bootloader provides a "bypass" mode of operation that essentially connects the SCI1 serial
communications peripheral of the freescale mcu to the EM250's serial Uart channel. This allows direct
communication to the EM250 radio for the purpose of firmware and radio configuration changes. Once
in bypass mode, the XCTU utility can change modem configuration and/or update EM250 firmware.
Bypass mode automatically handles any baud rate up to 115.2kbps. Note that this command is
unavailable when module is accessed remotely.
Update Firmware - "F"
The "F" command initiates a firmware download for both wired and over-the-air configurations.
Depending on the source of the command (received via Over the Air or local UART), the download will
proceed via wired or over-the-air respectively.
Adjust Timeout for Update Firmware - "T"
The "T" command changes the timeout before sending a NAK by Base-Time*2^(T). The Base-Time for
the local UART is different than the Base-Time for Over the Air. During a firmware update, the
bootloader will automatically increase the Timeout if repeat packets are received or multiple NAKs for
the same packet without success occur.
Application Version String - "A"
The "A" command provides the version of the currently loaded application. If no application is present,
"Unkown" will be returned.
Bootloader Version String - "V"
The "V" command provides the version of the currently loaded bootloader.
The version will return a string in the format BLFFF-HHH-XYZ_DDD where FFF represents the Flash size
in kilo bytes, HHH is the hardware, XYZ is the version, and DDD is the preferred XMODEM packet size
for updates. Double the preferred packet size is also possible, but not guaranteed. For example
"BL032-2B0-023_064" will take 64 byte CRC XMODEM payloads and may take 128 byte CRC XMODEM
payloads also. In this case, both 64 and 128 payloads are handled, but the 64 byte payload is
preferred for better Over the Air reliability.
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XBee®/XBee‐PRO®ZBRFModules
Firmware Updates
Wired Updates
A user can update their application using the bootloader in a wired configuration with the following
steps…
a. Plug XBee programmable module into a suitable serial port on a PC.
b. Open a hyperterminal (or similar dumb terminal application) session with 9600 baud, no parity,
and 8 data bits with one stop bit.
c. Hit Enter to display the bootloader menu.
d. Hit the "F" key to initiate a wired firmware update.
e. A series of "C" characters Will be displayed within the hyperterminal window. At this point,
select the "transfer->send file" menu item. Select the desired flat binary output file. (The file
should start at 0x8400 not 0x0000).
f. Select "Xmodem" as the protocol.
g. Click "Send" on the "Send File" dialog. The file will be downloaded to the XBee Programmable
module. Upon a successful update, the bootloader will jump to the newly loaded application.
Over-The-Air updates
A user can update their application using the bootloader in an "over-the-air" configuration with the
following steps…(This procedure assumes that the bootloader is running and not the application. The
EM250 baud rate must be set to 9600 baud. The bootloader only operates at 9600 baud. The
application must be programmed with some way to support returning to the bootloader in order to
support Over the Air (OTA) updates without local intervention.)
a. The XBee module sending the file OTA (Host module) should be set up with a series 2 Xbee
module with transparent mode firmware.
b. The XBee Programmable module receiving the update (remote module) is configured with API
firmware.
c. Open a hyperterminal session to the host module with 9600 baud, no parity, no hardwareflow
control, 8 data bits and 1 stop bit.
d.Enter 3 pluses "+++" to place the EM250 in command mode.
e. Set the Host Module destination address to the target module’s 64 bit address that the host
module will update (ATDH aabbccdd, ATDL eeffgghh, ATCN, where aabbccddeeffgghh is the hexadecimal 64 bit address of the target module).
f. Hit Enter and the bootloader command menu will be displayed from the remote module. (Note
that the option "B" doesn't exist for OTA)
g. Hit the "F" key to cause the remote module to request the new firmware file over-the-air.
h. The host module will begin receiving "C" characters indicating that the remote module is
requesting an Xmodem CRC transfer. Using XCTU or another terminal program, Select "XMODEM"
file transfer. Select the Binary file to upload/transfer. Click Send to start the transfer. At the conclusion of a successful transfer, the bootloader will jump to the newly loaded application.
Output File configuration
BKGD Programming
P&E Micro provides a background debug tool that allows flashing applications on the MC9S08QE parts
through their background debug mode port. By default, the Codewarrior tool produces an "ABS"
output file for use in programming parts through the background debug interface. The programmable
XBee from the factory has the BKGD debugging capability disabled. In order to debug, a bootloader
with the debug interface enabled needs to be loaded on the secondary processor or a stand-alone app
needs to be loaded.
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XBee®/XBee‐PRO®ZBRFModules
Bootloader updates
The supplied bootloader requires files in a "flat binary" format which differs from the default ABS file
produced. The Codewarrior tool also produces a S19 output file. In order to successfully flash new
applications, the S19 file must be converted into the flat binary format. Utilities are available on the
web that will convert S19 output to "BIN" outputs. Often times, the "BIN" file conversion will pad the
addresses from 0x0000 to the code space with the same number. (Often 0x00 or 0xFF) These extra
bytes before the APP code starts will need to be deleted from the bin file before the file can be
transferred to the bootloader.
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2.RFModuleOperation
DIN (data in)
DIN (data in)
DOUT (data out )
DOUT (data out)
Serial Communications
The XBee RF Modules interface to a host device through a logic-level asynchronous serial port. Through its serial
port, the module can communicate with any logic and voltage compatible UART; or through a level translator to any
serial device (for example: through a RS-232 or USB interface board).
UART Data Flow
Devices that have a UART interface can connect directly to the pins of the RF module as shown in the figure
below.
SystemDataFlowDiagraminaUART‐interfacedenvironment
Serial Data
(Low‐assertedsignalsdistinguishedwithhorizontallineoversignalname.)
Data enters the module UART through the DIN (pin 3) as an asynchronous serial signal. The signal should
idle high when no data is being transmitted.
Each data byte consists of a start bit (low), 8 data bits (least significant bit first) and a stop bit (high). The
following figure illustrates the serial bit pattern of data passing through the module.
UARTdatapacket0x1F(decimalnumberʺ31ʺ)astransmittedthroughtheRFmodule
ExampleDataFormatis8‐N‐1(bits‐parity‐#ofstopbits)
Serial communications depend on the two UARTs (the microcontroller's and the RF module's) to be
configured with compatible settings (baud rate, parity, start bits, stop bits, data bits).
The UART baud rate, parity, and stop bits settings on the XBee module can be configured with the BD, NB,
and SB commands respectively. See the command table in chapter 10 for details.
Serial Buffers
The XBee modules maintain small buffers to collect received serial and RF data, which is illustrated in the figure
below. The serial receive buffer collects incoming serial characters and holds them until they can be processed.
The serial transmit buffer collects data that is received via the RF link that will be transmitted out the UART.
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XBee®/XBee‐PRO®ZBRFModules
Serial
Receiver
Buffer
RF TX
Buffer
Transmitter
RF Switch
Antenna
Port
Receiver
Serial Transmit
Buffer
RF RX
Buffer
Processor
DIN
DOUT
CTS
RTS
TInternalDataFlowDiagram
Serial Receive Buffer
When serial data enters the RF module through the DIN Pin (pin 3), the data is stored in the serial receive
buffer until it can be processed. Under certain conditions, the module may not be able to process data in
the serial receive buffer immediately. If large amounts of serial data are sent to the module, CTS
control may be required to avoid overflowing the serial receive buffer.
Cases in which the serial receive buffer may become full and possibly overflow:
1. If the module is receiving a continuous stream of RF data, the data in the serial receive buffer
will not be transmitted until the module is no longer receiving RF data.
2. If the module is transmitting an RF data packet, the module may need to discover the destination address or establish a route to the destination. After transmitting the data, the module may
need to retransmit the data if an acknowledgment is not received, or if the transmission is a broadcast. These issues could delay the processing of data in the serial receive buffer.
flow
Serial Transmit Buffer
When RF data is received, the data is moved into the serial transmit buffer and sent out the UART. If the
serial transmit buffer becomes full enough such that all data in a received RF packet won’t fit in the serial
transmit buffer, the entire RF data packet is dropped.
Serial Flow Control
The RTS and CTS module pins can be used to provide RTS and/or CTS flow control. CTS flow control provides an
indication to the host to stop sending serial data to the module. RTS flow control allows the host to signal the
module to not send data in the serial transmit buffer out the uart. RTS
the D6 and D7 commands.
CTS Flow Control
If CTS flow control is enabled (D7 command), when the serial receive buffer is 17 bytes away from being
full, the module de-asserts CTS
re-asserted after the serial receive buffer has 34 bytes of space.
RTS Flow Control
If RTS flow control is enabled (D6 command), data in the serial transmit buffer will not be sent out the
DOUT pin as long as RTS
Cases in which the serial transmit buffer may become full resulting in dropped RF packets
1. If the RF data rate is set higher than the interface data rate of the module, the module could
receive data faster than it can send the data to the host.
2. If the host does not allow the module to transmit data out from the serial transmit buffer
because of being held off by hardware flow control.
and CTS flow control are enabled using
(sets it high) to signal to the host device to stop sending serial data. CTS is
is de-asserted (set high). The host device should not de-assert RTS for long
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XBee®/XBee‐PRO®ZBRFModules
periods of time to avoid filling the serial transmit buffer. If an RF data packet is received, and the serial
transmit buffer does not have enough space for all of the data bytes, the entire RF data packet will be
discarded.
Note: If the XBee is sending data out the UART when RTS
up to 5 characters out the UART after RTS
Serial Interface Protocols
The XBee modules support both transparent and API (Application Programming Interface) serial interfaces.
Transparent Operation
When operating in transparent mode, the modules act as a serial line replacement. All UART data received
through the DIN pin is queued up for RF transmission. When RF data is received, the data is sent out
through the DOUT pin. The module configuration parameters are configured using the AT command mode
interface.
Data is buffered in the serial receive buffer until one of the following causes the data to be packetized and
transmitted:
•No serial characters are received for the amount of time determined by the RO (Packetization Timeout) parameter. If RO = 0, packetization begins when a character is received.
•The Command Mode Sequence (GT + CC + GT) is received. Any character buffered in the serial
receive buffer before the sequence is transmitted.
•The maximum number of characters that will fit in an RF packet is received.
RF modules that contain the following firmware versions will support Transparent Mode:
20xx (AT coordinator), 22xx (AT router), and 28xx (AT end device).
is de-asserted (set high), the XBee could send
is de-asserted.
API Operation
API operation is an alternative to transparent operation. The frame-based API extends the level to which a
host application can interact with the networking capabilities of the module. When in API mode, all data
entering and leaving the module is contained in frames that define operations or events within the module.
Transmit Data Frames (received through the DIN pin (pin 3)) include:
•RF Transmit Data Frame
•Command Frame (equivalent to AT commands)
Receive Data Frames (sent out the DOUT pin (pin 2)) include:
•RF-received data frame
•Command response
•Event notifications such as reset, associate, disassociate, etc.
The API provides alternative means of configuring modules and routing data at the host application layer. A
host application can send data frames to the module that contain address and payload information instead
of using command mode to modify addresses. The module will send data frames to the application
containing status packets; as well as source, and payload information from received data packets.
The API operation option facilitates many operations such as the examples cited below:
-> Transmitting data to multiple destinations without entering Command Mode
-> Receive success/failure status of each transmitted RF packet
-> Identify the source address of each received packet
RF modules that contain the following firmware versions will support API operation: 21xx (API coordinator),
23xx (API router), and 29xx (API end device).
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A Comparison of Transparent and API Operation
The following table compares the advantages of transparent and API modes of operation:
Simple Interface All received serial data is transmitted unless the module is in command mode.
Easy to support It is easier for an application to support transparent operation and command mode
Easy to manage data
transmissions to multiple
destinations
Received data frames
indicate the sender's
address
Advanced ZigBee
addressing support
Advanced networking
diagnostics
Remote Configuration
Transparent Operation Features
API Operation Features
Transmitting RF data to multiple remotes only requires changing the address in the API frame. This
process is much faster than in transparent operation where the application must enter AT command
mode, change the address, exit command mode, and then transmit data.
Each API transmission can return a transmit status frame indicating the success or reason for
failure.
All received RF data API frames indicate the source address.
API transmit and receive frames can expose ZigBee addressing fields including source and
destination endpoints, cluster ID and profile ID. This makes it easy to support ZDO commands and
public profile traffic.
API frames can provide indication of IO samples from remote devices, and node identification
messages.
Set / read configuration commands can be sent to remote devices to configure them as needed
using the API.
As a general rule of thumb, API firmware is recommended when a device:
•sends RF data to multiple destinations
•sends remote configuration commands to manage devices in the network
•receives IO samples from remote devices
•receives RF data packets from multiple devices, and the application needs to know which device sent
which packet
•must support multiple ZigBee endpoints, cluster IDs, and/or profile IDs
•uses the ZigBee Device Profile services.
If the above conditions do not apply (e.g. a sensor node, router, or a simple application), then AT firmware
might be suitable. It is acceptable to use a mixture of devices running API and AT firmware in a network.
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16-bit Network
Address Discovery
Data Discarded
Successful
Transmi ssion
Yes
No
New
Transmission
16-bit Network
Add ress D iscovered ?
Route Known?
Rou te Dis covered ?
16-bit Network
Address Known?
Rou te Discovery
Transmit Data
Idle Mode
No
Yes
No No
Yes Yes
Modes of Operation
Idle Mode
When not receiving or transmitting data, the RF module is in Idle Mode. The module shifts into the other modes
of operation under the following conditions:
•Transmit Mode (Serial data in the serial receive buffer is ready to be packetized)
•Receive Mode (Valid RF data is received through the antenna)
•Sleep Mode (End Devices only)
•Command Mode (Command Mode Sequence is issued)
Transmit Mode
When serial data is received and is ready for packetization, the RF module will exit Idle Mode and attempt to
transmit the data. The destination address determines which node(s) will receive the data.
Prior to transmitting the data, the module ensures that a 16-bit network address and route to the destination
node have been established.
If the destination 16-bit network address is not known, network address discovery will take place. If a route is
not known, route discovery will take place for the purpose of establishing a route to the destination node. If a
module with a matching network address is not discovered, the packet is discarded. The data will be transmitted
once a route is established. If route discovery fails to establish a route, the packet will be discarded.
Tra n s mitModeSequence
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When data is transmitted from one node to another, a network-level acknowledgement is transmitted back
across the established route to the source node. This acknowledgement packet indicates to the source node that
the data packet was received by the destination node. If a network acknowledgement is not received, the
source node will re-transmit the data.
It is possible in rare circumstances for the destination to receive a data packet, but for the source to not receive
the network acknowledgment. In this case, the source will retransmit the data, which could cause the
destination to receive the same data packet multiple times. The XBee modules do not filter out duplicate
packets. The application should include provisions to address this potential issue
See Data Transmission and Routing in chapter 4 for more information.
Receive Mode
If a valid RF packet is received, the data is transferred to the serial transmit buffer.
Command Mode
To modify or read RF Module parameters, the module must first enter into Command Mode - a state in which
incoming serial characters are interpreted as commands. Refer to the API Mode section in chapter 9 for an
alternate means of configuring modules.
AT Command Mode
To Enter AT Command Mode:
Send the 3-character command sequence “+++” and observe guard times before and after the command characters. [Refer to the “Default AT Command Mode Sequence” below.]
Default AT Command Mode Sequence (for transition to Command Mode):
•No characters sent for one second [GT (Guard Times) parameter = 0x3E8]
•Input three plus characters (“+++”) within one second [CC (Command Sequence Character) parameter = 0x2B.]
•No characters sent for one second [GT (Guard Times) parameter = 0x3E8]
Once the AT command mode sequence has been issued, the module sends an "OK\r" out the DOUT pin. The
"OK\r" characters can be delayed if the module has not finished transmitting received serial data.
When command mode has been entered, the command mode timer is started (CT command), and the
module is able to receive AT commands on the DIN pin.
All of the parameter values in the sequence can be modified to reflect user preferences.
NOTE: Failure to enter AT Command Mode is most commonly due to baud rate mismatch. By default,
the BD (Baud Rate) parameter = 3 (9600 bps).
To Send AT Commands:
Send AT commands and parameters using the syntax shown below.
Figure2‐01.SyntaxforsendingATCommands
To read a parameter value stored in the RF module’s register, omit the parameter field.
The preceding example would change the RF module Destination Address (Low) to “0x1F”. To store the new
value to non-volatile (long term) memory, subsequently send the WR (Write) command.
For modified parameter values to persist in the module’s registry after a reset, changes must be saved to
non-volatile memory using the WR (Write) Command. Otherwise, parameters are restored to previously
saved values after the module is reset.
Command Response
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When a command is sent to the module, the module will parse and execute the command. Upon
successful execution of a command, the module returns an “OK” message. If execution of a command
results in an error, the module returns an “ERROR” message.
Applying Command Changes
Any changes made to the configuration command registers through AT commands will not take effect until
the changes are applied. For example, sending the BD command to change the baud rate will not change
the actual baud rate until changes are applied. Changes can be applied in one of the following ways:
•The AC (Apply Changes) command is issued.
•AT command mode is exited.
To Exit AT Command Mode:
1. Send the ATCN (Exit Command Mode) command (followed by a carriage return).
[OR]
2. If no valid AT Commands are received within the time specified by CT (Command Mode Timeout)
Command, the RF module automatically returns to Idle Mode.
For an example of programming the RF module using AT Commands and descriptions of each configurable parameter, please see the Command Reference Table chapter.
Sleep Mode
Sleep modes allow the RF module to enter states of low power consumption when not in use. The XBee RF
modules support both pin sleep (sleep mode entered on pin transition) and cyclic sleep (module sleeps for a
fixed time). XBee sleep modes are discussed in detail in chapter 6.
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3.XBeeZigBeeNetworks
Introduction to ZigBee
ZigBee is an open global standard built on the IEEE 802.15.4 MAC/PHY. ZigBee defines a network layer above the
802.15.4 layers to support advanced mesh routing capabilities. The ZigBee specification is developed by a growing
consortium of companies that make up the ZigBee Alliance. The Alliance is made up of over 300 members, including
semiconductor, module, stack, and software developers.
ZigBee Stack Layers
The ZigBee stack consists of several layers including the PHY, MAC, Network, Application Support Sublayer (APS),
and ZigBee Device Objects (ZDO) layers. Technically, an Application Framework (AF) layer also exists, but will be
grouped with the APS layer in remaining discussions. The ZigBee layers are shown in the figure below.
A description of each layer appears in the following table:
ZigBee Layer Description
PHY Defines the physical operation of the ZigBee device
MAC Manages RF data transactions between neighboring
Network Adds routing capabilities that allows RF data packets
APS (AF) Application layer that defines various addressing
ZDO Application layer that provides device and service
including receive sensitivity, channel rejection, output
power, number of channels, chip modulation, and
transmission rate specifications. Most ZigBee
applications operate on the 2.4 GHz ISM band at a
250kbps data rate. See the IEEE 802.15.4
specification for details.
devices (point to point). The MAC includes services
such as transmission retry and acknowledgment
management, and collision avoidance techniques
(CSMA-CA).
to traverse multiple devices (multiple "hops") to route
data from source to destination (peer to peer).
objects including profiles, clusters, and endpoints.
discovery features and advanced network
management capabilities.
Networking Concepts
Device Types
ZigBee defines three different device types: coordinator, router, and end device.
Node Types / Sample of a Basic ZigBee Network Topology
A coordinator has the following characteristics: it
•Selects a channel and PAN ID (both 64-bit and 16-bit) to start the network
•Can allow routers and end devices to join the network
•Can assist in routing data
•Cannot sleep--should be mains powered
•Can buffer RF data packets for sleeping end device children.
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A router has the following characteristics: it
•Must join a ZigBee PAN before it can transmit, receive, or route data
•After joining, can allow routers and end devices to join the network
•After joining, can assist in routing data
•Cannot sleep--should be mains powered.
•Can buffer RF data packets for sleeping end device children.
An end device has the following characteristics: it
•Must join a ZigBee PAN before it can transmit or receive data
•Cannot allow devices to join the network
•Must always transmit and receive RF data through its parent. Cannot route data.
•Can enter low power modes to conserve power and can be battery-powered.
An example of such a network is shown below:
In ZigBee networks, the coordinator must select a PAN ID (64-bit and 16-bit) and channel to start a network.
After that, it behaves essentially like a router. The coordinator and routers can allow other devices to join the
network and can route data.
After an end device joins a router or coordinator, it must be able to transmit or receive RF data through that
router or coordinator. The router or coordinator that allowed an end device to join becomes the "parent" of the
end device. Since the end device can sleep, the parent must be able to buffer or retain incoming data packets
destined for the end device until the end device is able to wake and receive the data.
PAN ID
ZigBee networks are called personal area networks or PANs. Each network is defined with a unique PAN
identifier (PAN ID). This identifier is common among all devices of the same network. ZigBee devices are either
preconfigured with a PAN ID to join, or they can discovery nearby networks and select a PAN ID to join.
ZigBee supports both a 64-bit and a 16-bit PAN ID. Both PAN IDs are used to uniquely identify a network.
Devices on the same ZigBee network must share the same 64-bit and 16-bit PAN IDs. If multiple ZigBee
networks are operating within range of each other, each should have unique PAN IDs.
The 16-bit PAN ID is used as a MAC layer addressing field in all RF data transmissions between devices in a
network. However, due to the limited addressing space of the 16-bit PAN ID (65,535 possibilities), there is a
possibility that multiple ZigBee networks (within range of each other) could use the same 16-bit PAN ID. To
resolve potential 16-bit PAN ID conflicts, the ZigBee Alliance created a 64-bit PAN ID.
The 64-bit PAN ID (also called the extended PAN ID), is intended to be a unique, non-duplicated value. When a
coordinator starts a network, it can either start a network on a preconfigured 64-bit PAN ID, or it can select a
random 64-bit PAN ID. The 64-bit PAN ID is used during joining; if a device has a preconfigured 64-bit PAN ID,
it will only join a network with the same 64-bit PAN ID. Otherwise, a device could join any detected PAN and
inherit the PAN ID from the network when it joins. The 64-bit PAN ID is included in all ZigBee beacons and is
used in 16-bit PAN ID conflict resolution.
Routers and end devices are typically configured to join a network with any 16-bit PAN ID as long as the 64-bit
PAN ID is valid. Coordinators typically select a random 16-bit PAN ID for their network.
Since the 16-bit PAN ID only allows up to 65,535 unique values, and since the 16-bit PAN ID is randomly
selected, provisions exist in ZigBee to detect if two networks (with different 64-bit PAN IDs) are operating on
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the same 16-bit PAN ID. If such a conflict is detected, the ZigBee stack can perform PAN ID conflict resolution to
change the 16-bit PAN ID of the network in order to resolve the conflict. See the ZigBee specification for details.
To summarize, ZigBee routers and end devices should be configured with the 64-bit PAN ID of the network they
want to join. They typically acquire the 16-bit PAN ID when they join a network.
Operating Channel
ZigBee utilizes direct-sequence spread spectrum modulation and operates on a fixed channel. The 802.15.4 PHY
defines 16 operating channels in the 2.4 GHz frequency band. XBee modules support all 16 channels and XBeePRO modules support 14 of the 16 channels.
ZigBee Application Layers: In Depth
This section provides a more in-depth look at the ZigBee application stack layers (APS, ZDO) including a discussion
on ZigBee endpoints, clusters, and profiles. Much of the material in this section can introduce unnecessary details of
the ZigBee stack that are not required in many cases.
Skip this section if
•The XBee does not need to interoperate or talk to non-Digi ZigBee devices
•The XBee simply needs to send data between devices.
Read this section if
•The XBee may talk to non-Digi ZigBee devices
•The XBee requires network management and discovery capabilities of the ZDO layer
•The XBee needs to operate in a public application profile (smart energy, home automation, etc.)
Application Support Sublayer (APS)
The APS layer in ZigBee adds support for application profiles, cluster IDs, and endpoints.
Application Profiles
Application profiles specify various device descriptions including required functionality for various devices. The
collection of device descriptions forms an application profile. Application profiles can be defined as "Public" or
"Private" profiles. Private profiles are defined by a manufacturer whereas public profiles are defined, developed,
and maintained by the ZigBee Alliance. Each application profile has a unique profile identifier assigned by the
ZigBee Alliance.
Examples of public profiles include:
•Home Automation
•Smart Energy
•Commercial Building Automation
The Smart Energy profile, for example, defines various device types including an energy service portal, load
controller, thermostat, in-home display, etc. The Smart Energy profile defines required functionality for each
device type. For example, a load controller must respond to a defined command to turn a load on or off. By
defining standard communication protocols and device functionality, public profiles allow interoperable ZigBee
solutions to be developed by independent manufacturers.
Digi XBee ZB firmware operates on a private profile called the Digi Drop-In Networking profile. However, the API
firmware in the module can be used in many cases to talk to devices in public profiles or non-Digi private
profiles. See the API Operations chapter for details.
Clusters
A cluster is an application message type defined within a profile. Clusters are used to specify a unique
function, service, or action. For example, the following are some clusters defined in the home automation
profile:
•On/Off - Used to switch devices on or off (lights, thermostats, etc.)
•Level Control - Used to control devices that can be set to a level between on and off
•Color Control - Controls the color of color capable devices.
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Each cluster has an associated 2-byte cluster identifier (cluster ID). The cluster ID is included in all
application transmissions. Clusters often have associated request and response messages. For example, a
smart energy gateway (service portal) might send a load control event to a load controller in order to
schedule turning on or off an appliance. Upon executing the event, the load controller would send a load
control report message back to the gateway.
Devices that operate in an application profile (private or public) must respond correctly to all required
clusters. For example, a light switch that will operate in the home automation public profile must correctly
implement the On/Off and other required clusters in order to interoperate with other home automation
devices. The ZigBee Alliance has defined a ZigBee Cluster Library (ZCL) that contains definitions or various
general use clusters that could be implemented in any profile.
XBee modules implement various clusters in the Digi private profile. In addition, the API can be used to
send or receive messages on any cluster ID (and profile ID or endpoint). See the Explicit Addressing ZigBee
Command API frame in chapter 3 for details.
Endpoints
The APS layer includes supports for endpoints. An endpoint can be thought of as a running application,
similar to a TCP/IP port. A single device can support one or more endpoints. Each application endpoint is
identified by a 1-byte value, ranging from 1 to 240. Each defined endpoint on a device is tied to an
application profile. A device could, for example, implement one endpoint that supports a Smart Energy load
controller, and another endpoint that supports other functionality on a private profile.
ZigBee Device Profile
Profile ID 0x0000 is reserved for the ZigBee Device Profile. This profile is implemented on all ZigBee
devices. Device Profile defines many device and service discovery features and network management
capabilities. Endpoint 0 is a reserved endpoint that supports the ZigBee Device Profile. This endpoint is
called the ZigBee Device Objects (ZDO) endpoint.
ZigBee Device Objects (ZDO)
The ZDO (endpoint 0) supports the discovery and management capabilities of the ZigBee Device Profile. A
complete listing of all ZDP services is included in the ZigBee specification. Each service has an associated
cluster ID.
The XBee ZB firmware allows applications to easily send ZDO messages to devices in the network using the
API. See the ZDO Transmissions section in chapter 4 for details.
Coordinator Operation
Forming a Network
The coordinator is responsible for selecting the channel, PAN ID (16-bit and 64-bit), security policy, and stack
profile for a network. Since a coordinator is the only device type that can start a network, each ZigBee network
must have one coordinator. After the coordinator has started a network, it can allow new devices to join the
network. It can also route data packets and communicate with other devices on the network.
To ensure the coordinator starts on a good channel and unused PAN ID, the coordinator performs a series of
scans to discover any RF activity on different channels (energy scan) and to discover any nearby operating PANs
(PAN scan). The process for selecting the channel and PAN ID are described in the following sections.
Channel Selection
When starting a network, the coordinator must select a "good" channel for the network to operate on. To do
this, it performs an energy scan on multiple channels (frequencies) to detect energy levels on each channel.
Channels with excessive energy levels are removed from its list of potential channels to start on.
PAN ID Selection
After completing the energy scan, the coordinator scans its list of potential channels (remaining channels after
the energy scan) to obtain a list of neighboring PANs. To do this, the coordinator sends a beacon request
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(broadcast) transmission on each potential channel. All nearby coordinators and routers (that have already
joined a ZigBee network) will respond to the beacon request by sending a beacon back to the coordinator. The
beacon contains information about the PAN the device is on, including the PAN identifiers (16-bit and 64-bit).
This scan (collecting beacons on the potential channels) is typically called an active scan or PAN scan.
After the coordinator completes the channel and PAN scan, it selects a random channel and unused 16-bit PAN
ID to start on.
Security Policy
The security policy determines which devices are allowed to join the network, and which device(s) can
authenticate joining devices. See chapter 5 for a detailed discussion of various security policies.
Persistent Data
Once a coordinator has started a network, it retains the following information through power cycle or reset
events:
•PAN ID
•Operating channel
•Security policy and frame counter values
•Child table (end device children that are joined to the coordinator).
The coordinator will retain this information indefinitely until it leaves the network. When the coordinator leaves
a network and starts a new network, the previous PAN ID, operating channel, and child table data are lost.
XBee ZB Coordinator Startup
The following commands control the coordinator network formation process.
Networkformationcommandsusedbythecoordinatortoformanetwork.
Command Description
ID Used to determine the 64-bit PAN ID. If set to 0 (default), a random 64-bit PAN ID will be selected.
SC Determines the scan channels bitmask (up to 16 channels) used by the coordinator when forming a
SD Set the scan duration period. This value determines how long the coordinator performs an energy scan or
ZS Set the ZigBee stack profile for the network.
EE Enable or disable security in the network.
NK Set the network security key for the network. If set to 0 (default), a random network security key will be
KY Set the trust center link key for the network. If set to 0 (default), a random link key will be used.
EO Set the security policy for the network.
Once the coordinator starts a network, the network configuration settings and child table data persist through
power cycles as mentioned in the "Persistent Data" section.
When the coordinator has successfully started a network, it
•Allows other devices to join the network for a time (see NJ command)
•Sets AI=0
•Starts blinking the Associate LED
•Sends an API modem status frame ("coordinator started") out the UART (API firmware only).
network. The coordinator will perform an energy scan on all enabled SC channels. It will then perform a
PAN ID scan and then form the network on one of the SC channels.
PAN ID scan on a given channel.
used.
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These behaviors are configurable using the following commands:
Command Description
NJ Sets the permit-join time on the coordinator,
D5 Enables the Associate LED functionality.
measured in seconds.
LT Sets the Associate LED blink time when
If any of the command values in the network formation commands table changes, the coordinator will leave its
current network and start a new network, possibly on a different channel. Note that command changes must be
applied (AC or CN command) before taking effect.
joined. Default is 1 blink per second.
Permit Joining
The permit joining attribute on the coordinator is configurable with the NJ command. NJ can be configured to
always allow joining, or to allow joining for a short time.
Joining Always Enabled
If NJ=0xFF (default), joining is permanently enabled. This mode should be used carefully. Once a network
has been deployed, the application should strongly consider disabling joining to prevent unwanted joins
from occurring.
Joining Temporarily Enabled
If NJ < 0xFF, joining will be enabled only for a number of seconds, based on the NJ parameter. The timer is
started once the XBee joins a network. Joining will not be re-enabled if the module is power cycled or reset.
The following mechanisms can restart the permit-joining timer:
•Changing NJ to a different value (and applying changes with the AC or CN commands)
•Pressing the commissioning button twice (enables joining for 1 minute)
•Issuing the CB command with a parameter of 2 (software emulation of a 2 button press - enables
joining for 1 minute).
Resetting the Coordinator
When the coordinator is reset or power cycled, it checks its PAN ID, operating channel and stack profile against
the network configuration settings (ID, CH, ZS). It also verifies the saved security policy against the security
configuration settings (EE, NK, KY). If the coordinator's PAN ID, operating channel, stack profile, or security
policy is not valid based on its network and security configuration settings, then the coordinator will leave the
network and attempt to form a new network based on its network formation command values.
To prevent the coordinator from leaving an existing network, the WR command should be issued after all
network formation commands have been configured in order to retain these settings through power cycle or
reset events.
Leaving a Network
There are a couple of mechanisms that will cause the coordinator to leave its current PAN and start a new
network based on its network formation parameter values. These include the following:
•Change the ID command such that the current 64-bit PAN ID is invalid.
•Change the SC command such that the current channel (CH) is not included in the channel mask.
•Change the ZS or any of the security command values (excluding NK).
•Issue the NR0 command to cause the coordinator to leave.
•Issue the NR1 command to send a broadcast transmission, causing all devices in the network to leave and
migrate to a different channel.
•Press the commissioning button 4 times or issue the CB command with a parameter of 4.
•Issue a network leave command.
Note that changes to ID, SC, ZS, and security command values only take effect when changes are applied (AC
or CN commands).
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Replacing a Coordinator (Security Disabled Only)
In rare occasions, it may become necessary to replace an existing coordinator in a network with a new physical
device. If security is not enabled in the network, a replacement XBee coordinator can be configured with the
PAN ID (16-bit and 64-bit), channel, and stack profile settings of a running network in order to replace an
existing coordinator.
NOTE: Having two coordinators on the same channel, stack profile, and PAN ID (16-bit and 64-bit) can cause
problems in the network and should be avoided. When replacing a coordinator, the old coordinator should be
turned off before starting the new coordinator.
To replace a coordinator, the following commands should be read from a device on the network:
AT C o m m a nd Description
OP Read the operating 64-bit PAN
OI Read the operating 16-bit PAN
CH Read the operating channel.
ZS Read the stack profile.
ID.
ID.
Each of the commands listed above can be read from any device on the network. (These parameters will be the
same on all devices in the network.) After reading these commands from a device on the network, these
parameter values should be programmed into the new coordinator using the following commands.
AT C o m m a nd Description
ID Set the 64-bit PAN ID to match
II Set the initial 16-bit PAN ID to
SC Set the scan channels bitmask
ZS Set the stack profile to match the
Note: II is the initial 16-bit PAN ID. Under certain conditions, the ZigBee stack can change the 16-bit PAN ID of
the network. For this reason, the II command cannot be saved using the WR command. Once II is set, the
coordinator leaves the network and starts on the 16-bit PAN ID specified by II.
the read OP value.
match the read OI value.
to enable the read operating
channel (CH command). For
example, if the operating
channel is 0x0B, set SC to
0x0001. If the operating channel
is 0x17, set SC to 0x1000.
read ZS value.
Example: Starting a Coordinator
1. Set SC and ID to the desired scan channels and PAN ID values. (The defaults should suffice.)
2. If SC or ID is changed from the default, issue the WR command to save the changes.
3. If SC or ID is changed from the default, apply changes (make SC and ID changes take effect)
either by sending the AC command or by exiting AT command mode.
4. The Associate LED will start blinking once the coordinator has selected a channel and PAN ID.
5. The API Modem Status frame ("Coordinator Started") is sent out the UART (API firmware only).
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6. Reading the AI command (association status) will return a value of 0, indicating a successful
startup.
7. Reading the MY command (16-bit address) will return a value of 0, the ZigBee-defined 16-bit
address of the coordinator.
After startup, the coordinator will allow joining based on its NJ value.
Example: Replacing a Coordinator (security disabled)
1. Read the OP, OI, CH, and ZS commands on the running coordinator.
2. Set the ID, SC, and ZS parameters on the new coordinator, followed by WR command to save
these parameter values.
3. Turn off the running coordinator.
4. Set the II parameter on the new coordinator to match the read OI value on the old coordinator.
5. Wait for the new coordinator to start (AI=0).
Router Operation
Routers must discover and join a valid ZigBee network before they can participate in a ZigBee network. After a
router has joined a network, it can allow new devices to join the network. It can also route data packets and
communicate with other devices on the network.
Discovering ZigBee Networks
To discover nearby ZigBee networks, the router performs a PAN (or active) scan, just like the coordinator does
when it starts a network. During the PAN scan, the router sends a beacon request (broadcast) transmission on
the first channel in its scan channels list. All nearby coordinators and routers operating on that channel (that are
already part of a ZigBee network) respond to the beacon request by sending a beacon back to the router. The
beacon contains information about the PAN the nearby device is on, including the PAN identifier (PAN ID), and
whether or not joining is allowed. The router evaluates each beacon received on the channel to determine if a
valid PAN is found. A router considers a PAN to be valid if the PAN:
•Has a valid 64-bit PAN ID (PAN ID matches ID if ID > 0)
•Has the correct stack profile (ZS command)
•Is allowing joining.
If a valid PAN is not found, the router performs the PAN scan on the next channel in its scan channels list and
continues scanning until a valid network is found, or until all channels have been scanned. If all channels have
been scanned and a valid PAN was not discovered, all channels will be scanned again.
The ZigBee Alliance requires that certified solutions not send beacon request messages too frequently. To meet
certification requirements, the XBee firmware attempts 9 scans per minute for the first 5 minutes, and 3 scans
per minute thereafter. If a valid PAN is within range of a joining router, it should typically be discovered within a
few seconds.
Joining a Network
Once the router discovers a valid network, it sends an association request to the device that sent a valid beacon
requesting a join on the ZigBee network. The device allowing the join then sends an association response frame
that either allows or denies the join.
When a router joins a network, it receives a 16-bit address from the device that allowed the join. The 16-bit
address is randomly selected by the device that allowed the join.
Authentication
In a network where security is enabled, the router must then go through an authentication process. See the
Security chapter for a discussion on security and authentication.
After the router is joined (and authenticated, in a secure network), it can allow new devices to join the network.
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Persistent Data
Once a router has joined a network, it retains the following information through power cycle or reset events:
•PAN ID
•Operating channel
•Security policy and frame counter values
•Child table (end device children that are joined to the coordinator).
The router will retain this information indefinitely until it leaves the network. When the router leaves a network,
the previous PAN ID, operating channel, and child table data are lost.
XBee ZB Router Joining
When the router is powered on, if it is not already joined to a valid ZigBee network, it immediately attempts to
find and join a valid ZigBee network.
Note: The DJ command can be set to 1 to disable joining. The DJ parameter cannot be written with WR, so a
power cycle always clears the DJ setting.
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The following commands control the router joining process.
Command Description
ID Sets the 64-bit PAN ID to join. Setting ID=0 allows the router to join any
64-bit PAN ID.
SC Set the scan channels bitmask that determines which channels a router
SD Set the scan duration, or time that the router will listen for beacons on
ZS Set the stack profile on the device.
EE Enable or disable security in the network. This must be set to match the
KY Set the trust center link key. If set to 0 (default), the link key is expected to
will scan to find a valid network. SC on the router should be set to match
SC on the coordinator. For example, setting SC to 0x281 enables
scanning on channels 0x0B, 0x12, and 0x14, in that order.
each channel.
EE value (security policy) of the coordinator.
be obtained (unencrypted) during joining.
Once the router joins a network, the network configuration settings and child table data persist through power
cycles as mentioned in the "Persistent Data" section previously. If joining fails, the status of the last join
attempt can be read in the AI command register.
If any of the above command values change, when command register changes are applied (AC or CN
commands), the router will leave its current network and attempt to discover and join a new valid network.
When a ZB router has successfully joined a network, it:
•Allows other devices to join the network for a time
•Sets AI=0
•Starts blinking the Associate LED
•Sends an API modem status frame ("associated") out the UART (API firmware only).
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These behaviors are configurable using the following commands:
Command Description
NJ Sets the permit-join time on
D5 Enables the Associate LED
LT Sets the Associate LED blink
Permit Joining
The permit joining attribute on the router is configurable with the NJ command. NJ can be configured to always
allow joining, or to allow joining for a short time.
Joining Always Enabled
the router, or the time that it
will allow new devices to join
the network, measured in
seconds. If NJ=0xFF, permit
joining will always be enabled.
functionality.
time when joined. Default is 2
blinks per second (router).
If NJ=0xFF (default), joining is permanently enabled. This mode should be used carefully. Once a network has
been deployed, the application should strongly consider disabling joining to prevent unwanted joins from
occurring.
Joining Temporarily Enabled
If NJ < 0xFF, joining will be enabled only for a number of seconds, based on the NJ parameter. The timer is
started once the XBee joins a network. Joining will not be re-enabled if the module is power cycled or reset. The
following mechanisms can restart the permit-joining timer:
•Changing NJ to a different value (and applying changes with the AC or CN commands)
•Pressing the commissioning button twice (enables joining for 1 minute)
•Issuing the CB command with a parameter of 2 (software emulation of a 2 button press - enables joining
for 1 minute)
•Causing the router to leave and rejoin the network.
Router Network Connectivity
Once a router joins a ZigBee network, it remains connected to the network on the same channel and PAN ID as
long as it is not forced to leave. (See Leaving a Network section for details.) If the scan channels (SC), PAN ID
(ID) and security settings (EE, KY) do not change after a power cycle, the router will remain connected to the
network after a power cycle.
If a router may physically move out of range of the network it initially joined, the application should include
provisions to detect if the router can still communicate with the original network. If communication with the
original network is lost, the application may choose to force the router to leave the network (see Leaving a
Network section for details). The XBee firmware includes two provisions to automatically detect the presence of
a network, and leave if the check fails.
Power-On Join Verification
The JV command (join verification) enables the power-on join verification check. If enabled, the XBee will
attempt to discover the 64-bit address of the coordinator when it first joins a network. Once it has joined, it
will also attempt to discover the 64-bit address of the coordinator after a power cycle event. If 3 discovery
attempts fail, the router will leave the network and try to join a new network. Power-on join verification is
disabled by default (JV defaults to 0).
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Network Watchdog
The NW command (network watchdog timeout) can be used for a powered router to periodically check for
the presence of a coordinator to verify network connectivity. The NW command specifies a timeout in
minutes where the router must receive communication from the coordinator or data collector. The following
events restart the network watchdog timer:
•RF data received from the coordinator
•RF data sent to the coordinator and an acknowledgment was received
•Many-to-one route request was received (from any device)
•Changing the value of NW.
If the watchdog timer expires (no valid data received for NW time), the router will attempt to discover the
64-bit address of the coordinator. If the address cannot be discovered, the router records one watchdog
timeout. Once three consecutive network watchdog timeouts have expired (3 * NW) and the coordinator
has not responded to the address discovery attempts, the router will leave the network and attempt to join
a new network. Anytime a router receives valid data from the coordinator or data collector, it will clear the
watchdog timeouts counter and restart the watchdog timer. The watchdog timer (NW command) is settable
to several days. The network watchdog feature is disabled by default (NW defaults to 0).
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Clear Network Watchdog Failure Count
Restart Network Watchdog Timer
Received RF
Communi cation from
Coordinator or Data
Collector
Yes
Network Watchdog
Timer Expired?
No
No
Discover Coordinator
Yes
Coordinator
Found?
Yes
Network Watchdog Failure
Count +=1
No
Network
Watchdog
Failure Count
=3 ?
Leave
Yes
No
Network Watchdog Behavior
Leaving a Network
There are a couple of mechanisms that will cause the router to leave its current PAN and attempt to discover
and join a new network based on its network joining parameter values.
These include the following:
•Change the ID command such that the current 64-bit PAN ID is invalid.
•Change the SC command such that the current channel (CH) is not included in the channel mask.
•Change the ZS or any of the security command values.
•Issue the NR0 command to cause the router to leave.
•Issue the NR1 command to send a broadcast transmission, causing all devices in the network to leave and
migrate to a different channel.
•Press the commissioning button 4 times or issue the CB command with a parameter of 4.
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•Issue a network leave command.
Note that changes to ID, SC, ZS, and security command values only take effect when changes are applied (AC
or CN commands).
Resetting the Router
When the router is reset or power cycled, it checks its PAN ID, operating channel and stack profile against the
network configuration settings (ID, SC, ZS). It also verifies the saved security policy is valid based on the
security configuration commands (EE, KY). If the router's PAN ID, operating channel, stack profile, or security
policy is invalid, the router will leave the network and attempt to join a new network based on its network
joining command values.
To prevent the router from leaving an existing network, the WR command should be issued after all network
joining commands have been configured in order to retain these settings through power cycle or reset events.
Example: Joining a Network
After starting a coordinator (that is allowing joins), the following steps will cause a router to join the network:
1. Set ID to the desired 64-bit PAN ID, or to 0 to join any PAN.
2. Set SC to the list of channels to scan to find a valid network.
3. If SC or ID is changed from the default, apply changes (make SC and ID changes take effect)
by issuing the AC or CN command.
4. The Associate LED will start blinking once the router has joined a PAN.
5. If the Associate LED is not blinking, the AI command can be read to determine the cause of join
failure.
6. Once the router has joined, the OP and CH commands will indicate the operating 64-bit PAN ID
and channel the router joined.
7. The MY command will reflect the 16-bit address the router received when it joined.
8. The API Modem Status frame ("Associated") is sent out the UART (API firmware only).
9. The joined router will allow other devices to join for a time based on its NJ setting.
End Device Operation
Similar to routers, end devices must also discover and join a valid ZigBee network before they can participate in
a network. After an end device has joined a network, it can communicate with other devices on the network.
Since end devices are intended to be battery powered and therefore support low power (sleep) modes, end
devices cannot allow other devices to join, nor can they route data packets.
Discovering ZigBee Networks
End devices go through the same process as routers to discover networks by issuing a PAN scan. After sending
the broadcast beacon request transmission, the end device listens for a short time in order to receive beacons
sent by nearby routers and coordinators on the same channel. The end device evaluates each beacon received
on the channel to determine if a valid PAN is found. An end device considers a PAN to be valid if the PAN:
•Has a valid 64-bit PAN ID (PAN ID matches ID if ID > 0)
•Has the correct stack profile (ZS command)
•Is allowing joining
•Has capacity for additional end devices (see End Device Capacity section below).
If a valid PAN is not found, the end device performs the PAN scan on the next channel in its scan channels list
and continues this process until a valid network is found, or until all channels have been scanned. If all channels
have been scanned and a valid PAN was not discovered, the end device may enter a low power sleep state and
scan again later.
If scanning all SC channels fails to discover a valid PAN, XBee ZB modules will attempt to enter a low power
state and will retry scanning all SC channels after the module wakes from sleeping. If the module cannot enter
a low power state, it will retry scanning all channels, similar to the router. To meet ZigBee Alliance
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requirements, the end device will attempt up to 9 scans per minute for the first 5 minutes, and 3 scans per
minute thereafter.
Note: The XBee ZB end device will not enter sleep until it has completed scanning all SC channels for a valid
network.
Joining a Network
Once the end device discovers a valid network, it joins the network, similar to a router, by sending an
association request (to the device that sent a valid beacon) to request a join on the ZigBee network. The device
allowing the join then sends an association response frame that either allows or denies the join.
When an end device joins a network, it receives a 16-bit address from the device that allowed the join. The 16bit address is randomly selected by the device that allowed the join.
Parent Child Relationship
Since an end device may enter low power sleep modes and not be immediately responsive, the end device relies
on the device that allowed the join to receive and buffer incoming messages in its behalf until it is able to wake
and receive those messages. The device that allowed an end device to join becomes the parent of the end
device, and the end device becomes a child of the device that allowed the join.
End Device Capacity
Routers and coordinators maintain a table of all child devices that have joined called the child table. This table is
a finite size and determines how many end devices can join. If a router or coordinator has at least one unused
entry in its child table, the device is said to have end device capacity. In other words, it can allow one or more
additional end devices to join. ZigBee networks should have sufficient routers to ensure adequate end device
capacity.
In the XBee ZB 2x6x firmware, a coordinator can support 10 end devices, and a router can support 12 end
devices.
In ZB firmware, the NC command (number of remaining end device children) can be used to determine how
many additional end devices can join a router or coordinator. If NC returns 0, then the router or coordinator
device has no more end device capacity. (Its child table is full.)
Also of note, since routers cannot sleep, there is no equivalent need for routers or coordinators to track joined
routers. Therefore, there is no limit to the number of routers that can join a given router or coordinator device.
(There is no "router capacity" metric.)
Authentication
In a network where security is enabled, the end device must then go through an authentication process. See
chapter 5 for a discussion on security and authentication.
Persistent Data
The end device can retain its PAN ID, operating channel, and security policy information through a power cycle.
However, since end devices rely heavily on a parent, the end device does an orphan scan to try and contact its
parent. If the end device does not receive an orphan scan response (called a coordinator realignment
command), it will leave the network and try to discover and join a new network. When the end device leaves a
network, the previous PAN ID and operating channel settings are lost.
Orphan Scans
When an end device comes up from a power cycle, it performs an orphan scan to verify it still has a valid parent.
The orphan scan is sent as a broadcast transmission and contains the 64-bit address of the end device. Nearby
routers and coordinator devices that receive the broadcast check their child tables for an entry that contains the
end device's 64-bit address. If an entry is found with a matching 64-bit address, the device sends a coordinator
realignment command to the end device that includes the end device's 16-bit address, 16-bit PAN ID, operating
channel, and the parent's 64-bit and 16-bit addresses.
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If the orphaned end device receives a coordinator realignment command, it is considered joined to the network.
Otherwise, it will attempt to discover and join a valid network.
XBee: ZB End Device Joining
When an end device is powered on, if it is not joined to a valid ZigBee network, or if the orphan scan fai ls to find
a parent, it immediately attempts to find and join a valid ZigBee network.
Note: The DJ command can be set to 1 to disable joining. The DJ parameter cannot be written with WR, so a
power cycle always clears the DJ setting.
Similar to a router, the following commands control the end device joining process.
Networkjoiningcommandsusedbyanenddevicetojoinanetwork.
Command Description
ID Sets the 64-bit PAN ID to join. Setting ID=0 allows the router
SC Set the scan channels bitmask that determines which
SD Set the scan duration, or time that the end device will listen
ZS Set the stack profile on the device.
EE Enable or disable security in the network. This must be set to
KY Set the trust center link key. If set to 0 (default), the link key
to join any 64-bit PAN ID.
channels an end device will scan to find a valid network. SC
on the end device should be set to match SC on the
coordinator and routers in the desired network. For example,
setting SC to 0x281 enables scanning on channels 0x0B,
0x12, and 0x14, in that order.
for beacons on each channel.
match the EE value (security policy) of the coordinator.
is expected to be obtained (unencrypted) during joining.
Once the end device joins a network, the network configuration settings can persist through power cycles as
mentioned in the "Persistent Data" section previously. If joining fails, the status of the last join attempt can be
read in the AI command register.
If any of these command values changes, when command register changes are applied, the end device will
leave its current network and attempt to discover and join a new valid network.
When a ZB end device has successfully started a network, it
•Sets AI=0
•Starts blinking the Associate LED
•Sends an API modem status frame ("associated") out the UART (API firmware only)
•Attempts to enter low power modes.
These behaviors are configurable using the following commands:
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Command Description
D5 Enables the Associate LED functionality.
LT Sets the Associate LED blink time when joined. Default is 2 blinks per
SM, SP, ST, SN, SOParameters that configure the sleep mode characteristics. (See
second (end devices).
Managing End Devices chapter for details.)
Parent Connectivity
The XBee ZB end device sends regular poll transmissions to its parent when it is awake. These poll
transmissions query the parent for any new received data packets. The parent always sends a MAC layer
acknowledgment back to the end device. The acknowledgment indicates whether the parent has data for the
end device or not.
If the end device does not receive an acknowledgment for 3 consecutive poll requests, it considers itself
disconnected from its parent and will attempt to discover and join a valid ZigBee network. See "Managing End
Devices" chapter for details.
Resetting the End Device
When the end device is reset or power cycled, if the orphan scan successfully locates a parent, the end device
then checks its PAN ID, operating channel and stack profile against the network configuration settings (ID, SC,
ZS). It also verifies the saved security policy is valid based on the security configuration commands (EE, KY). If
the end device's PAN ID, operating channel, stack profile, or security policy is invalid, the end device will leave
the network and attempt to join a new network based on its network joining command values.
To prevent the end device from leaving an existing network, the WR command should be issued after all
network joining commands have been configured in order to retain these settings through power cycle or reset
events.
Leaving a Network
There are a couple of mechanisms that will cause the router to leave its current PAN and attempt to discover
and join a new network based on its network joining parameter values. These include the following:
•The ID command changes such that the current 64-bit PAN ID is invalid.
•The SC command changes such that the current operating channel (CH) is not included in the channel
mask.
•The ZS or any of the security command values change.
•The NR0 command is issued to cause the end device to leave.
•The NR1 command is issued to send a broadcast transmission, causing all devices in the network to leave
and migrate to a different channel.
•The commissioning button is pressed 4 times or the CB command is issued with a parameter of 4.
•The end device's parent is powered down or the end device is moved out of range of the parent such that
the end device fails to receive poll acknowledgment messages.
Note that changes to command values only take effect when changes are applied (AC or CN commands).
Example: Joining a Network
After starting a coordinator (that is allowing joins), the following steps will cause an XBee end device to join the
network:
1. Set ID to the desired 64-bit PAN ID, or to 0 to join any PAN.
2. Set SC to the list of channels to scan to find a valid network.
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3. If SC or ID is changed from the default, apply changes (make SC and ID changes take effect)
by issuing the AC or CN command.
4. The Associate LED will start blinking once the end device has joined a PAN.
5. If the Associate LED is not blinking, the AI command can be read to determine the cause of join
failure.
6. Once the end device has joined, the OP and CH commands will indicate the operating 64-bit
PAN ID and channel the end device joined.
7. The MY command will reflect the 16-bit address the router received when it joined.
8. The API Modem Status frame ("Associated") is sent out the UART (API firmware only).
9. The joined end device will attempt to enter low power sleep modes based on its sleep
configuration commands (SM, SP, SN, ST, SO).
Channel Scanning
As mentioned previously, routers and end devices must scan one or more channels to discover a valid network
to join. When a join attempt begins, the XBee sends a beacon request transmission on the lowest channel
specified in the SC (scan channels) command bitmask. If a valid PAN is found on the channel, the XBee will
attempt to join the PAN on that channel. Otherwise, if a valid PAN is not found on the channel, it will attempt
scanning on the next higher channel in the SC command bitmask. The XBee will continue to scan each channel
(from lowest to highest) in the SC bitmask until a valid PAN is found or all channels have been scanned. Once all
channels have been scanned, the next join attempt will start scanning on the lowest channel specified in the SC
command bitmask.
For example, if the SC command is set to 0x400F, the XBee would start scanning on channel 11 (0x0B) and scan
until a valid beacon is found, or until channels 11, 12, 13, 14, and 25 have been scanned (in that order).
Once an XBee router or end device joins a network on a given channel, if the XBee is told to leave (see "Leaving
a Network" section), it will leave the channel it joined on and continue scanning on the next higher channel in
the SC bitmask.
For example, if the SC command is set to 0x400F, and the XBee joins a PAN on channel 12 (0x0C), if the XBee
leaves the channel, it will start scanning on channel 13, followed by channels 14 and 25 if a valid network is not
found. Once all channels have been scanned, the next join attempt will start scanning on the lowest channel
specified in the SC command bitmask.
Managing Multiple ZigBee Networks
In some applications, multiple ZigBee networks may exist in proximity of each other. The application may need
provisions to ensure the XBee joins the desired network. There are a number of features in ZigBee to manage
joining among multiple networks. These include the following:
•PAN ID Filtering
•Preconfigured Security Keys
•Permit Joining
•Application Messaging
PAN ID Filtering
The XBee can be configured with a fixed PAN ID by setting the ID command to a non-zero value. If the PAN ID
is set to a non-zero value, the XBee will only join a network with the same PAN ID.
Preconfigured Security Keys
Similar to PAN ID filtering, this method requires a known security key be installed on a router to ensure it will
join a ZigBee network with the same security key. If the security key (KY command) is set to a non-zero value,
and if security is enabled (EE command), an XBee router or end device will only join a network with the same
security key.
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Permit Joining
The Permit Joining parameter can be disabled in a network to prevent unwanted devices from joining. When a
new device must be added to a network, permit-joining can be enabled for a short time on the desired network.
In the XBee firmware, joining is disabled by setting the NJ command to a value less than 0xFF on all routers and
coordinator devices. Joining can be enabled for a short time using the commissioning push-button (see Network
Commissioning chapter for details) or the CB command.
Application Messaging
If the above mechanisms are not feasible, the application could build in a messaging framework between the
coordinator and devices that join its network. For example, the application code in joining devices could send a
transmission to the coordinator after joining a network, and wait to receive a defined reply message. If the
application does not receive the expected response message after joining, the application could force the XBee
to leave and continue scanning (see NR parameter).
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4.Transmission,Addressing,andRouting
Addressing
All ZigBee devices have two different addresses, a 64-bit and a 16-bit address. The characteristics of each are
described below.
64-bit Device Addresses
The 64-bit address is a unique device address assigned during manufacturing. This address is unique to each
physical device. The 64-bit address includes a 3-byte Organizationally Unique Identifier (OUI) assigned by the
IEEE. The 64-bit address is also called the extended address.
16-bit Device Addresses
A device receives a 16-bit address when it joins a ZigBee network. For this reason, the 16-bit address is also
called the "network address". The 16-bit address of 0x0000 is reserved for the coordinator. All other devices
receive a randomly generated address from the router or coordinator device that allows the join. The 16-bit
address can change under certain conditions:
•An address conflict is detected where two devices are found to have the same 16-bit address
•A device leaves the network and later joins (it can receive a different address)
All ZigBee transmissions are sent using the source and destination 16-bit addresses. The routing tables on
ZigBee devices also use 16-bit addresses to determine how to route data packets through the network.
However, since the 16-bit address is not static, it is not a reliable way to identify a device.
To solve this problem, the 64-bit destination address is often included in data transmissions to guarantee data is
delivered to the correct destination. The ZigBee stack can discover the 16-bit address, if unknown, before
transmitting data to a remote.
Application Layer Addressing
ZigBee devices can support multiple application profiles, cluster IDs, and endpoints. (See "ZigBee Application
Layers - In Depth" in chapter 3.) Application layer addressing allows data transmissions to be addressed to
specific profile IDs, cluster IDs, and endpoints. Application layer addressing is useful if an application must
•Interoperate with other ZigBee devices outside of the Digi application profile
•Utilize service and network management capabilities of the ZDO
•Operate on a public application profile such as Home Controls or Smart Energy.
The API firmware provides a simple yet powerful interface that can easily send data to any profile ID, endpoint,
and cluster ID combination on any device in a ZigBee network.
Data Transmission
ZigBee data packets can be sent as either unicast or broadcast transmissions. Unicast transmissions route data from
one source device to one destination device, whereas broadcast transmissions are sent to many or all devices in the
network.
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C
R
R
E
R
E
R
E
E
R
E
R
Legend
C=Coordinator
R=R outer
E=End D evi ce
E
Broadcast Transmissions
Broadcast transmissions within the ZigBee protocol are intended to be propagated throughout the entire
network such that all nodes receive the transmission. To accomplish this, the coordinator and all routers that
receive a broadcast transmission will retransmit the packet three times.
Note: when a router or coordinator delivers a broadcast transmission to an end device child, the transmission is
only sent once (immediately after the end device wakes and polls the parent for any new data). See Parent
Operation section in chapter 6 for details.
BroadcastDataTran s m ission
©2011DigiInternational,Inc. 54
Each node that transmits the broadcast will also create an entry in a local broadcast transmission table. This
entry is used to keep track of each received broadcast packet to ensure the packets are not endlessly
transmitted. Each entry persists for 8 seconds. The broadcast transmission table holds 8 entries.
For each broadcast transmission, the ZigBee stack must reserve buffer space for a copy of the data packet. This
copy is used to retransmit the packet as needed. Large broadcast packets will require more buffer space. This
information on buffer space is provided for general knowledge; the user does not and cannot change any buffer
spacing. Buffer spacing is handled automatically by the XBee module.
Since broadcast transmissions are retransmitted by each device in the network, broadcast messages should be
used sparingly.
Unicast Transmissions
Unicast transmissions are sent from one source device to another destination device. The destination device
could be an immediate neighbor of the source, or it could be several hops away. Unicast transmissions that are
sent along a multiple hop path require some means of establishing a route to the destination device. See the
"RF Packet Routing" section in chapter 4 for details.
Address Resolution
As mentioned previously, each device in a ZigBee network has both a 16-bit (network) address and a 64-bit
(extended) address. The 64-bit address is unique and assigned to the device during manufacturing, and the
XBee®/XBee‐PRO®ZBRFModules
16-bit address is obtained after joining a network. The 16-bit address can also change under certain
conditions.
When sending a unicast transmission, the ZigBee network layer uses the 16-bit address of the destination
and each hop to route the data packet. If the 16-bit address of the destination is not known, the ZigBee
stack includes a discovery provision to automatically discover the destination device's 16-bit address before
routing the data.
To discover a 16-bit address of a remote, the device initiating the discovery sends a broadcast address
discovery transmission. The address discovery broadcast includes the 64-bit address of the remote device
whose 16-bit address is being requested. All nodes that receive this transmission check the 64-bit address
in the payload and compare it to their own 64-bit address. If the addresses match, the device sends a
response packet back to the initiator. This response includes the remote's 16-bit address. When the
discovery response is received, the initiator will then transmit the data.
Address Table
Each ZigBee device maintains an address table that maps a 64-bit address to a 16-bit address. When a
transmission is addressed to a 64-bit address, the ZigBee stack searches the address table for an entry
with a matching 64-bit address, in hopes of determining the destination's 16-bit address. If a known 16-bit
address is not found, the ZigBee stack will perform address discovery to discover the device's current 16-
bit address.
SampleAddressTabl e
64-bit Address 16-bit Address
0013 A200 4000 0001 0x4414
0013 A200 400A 3568 0x1234
0013 A200 4004 1122 0xC200
0013 A200 4002 1123 0xFFFE (unknown)
The XBee modules can store up to 10 address table entries. For applications where a single device (e.g.
coordinator) may send unicast transmissions to more than 10 devices, the application should implement an
address table to store the 16-bit and 64-bit addresses for each remote device. Any XBee that will send data
to more than 10 remotes should also use API firmware. The application can then send both the 16-bit and
64-bit addresses to the XBee in the API transmit frames which will significantly reduce the number of 16-bit
address discoveries and greatly improve data throughput.
If an application will support an address table, the size should ideally be larger than the maximum number
of destination addresses the device will communicate with. Each entry in the address table should contain a
64-bit destination address and its last known 16-bit address.
When sending a transmission to a destination 64-bit address, the application should search the address
table for a matching 64-bit address. If a match is found, the 16-bit address should be populated into the
16-bit address field of the API frame. If a match is not found, the 16-bit address should be set to 0xFFFE
(unknown) in the API transmit frame.
The API provides indication of a remote device's 16-bit address in the following frames:
•All receive data frames
Rx Data (0x90)
Rx Explicit Data (0x91)
IO Sample Data (0x92)
Node Identification Indicator (0x95)
Route Record Indicator (0xA1)
etc.
•Transmit status frame (0x8B)
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The application should always update the 16-bit address in the address table when one of these frames is
received to ensure the table has the most recently known 16-bit address. If a transmission failure occurs,
the application should set the 16-bit address in the table to 0xFFFE (unknown).
Fragmentation
Each unicast transmission may support up to 84 bytes of RF payload. (Enabling security or using source
routing can reduce this number. See the NP command for details.) However, the XBee ZB firmware supports
a ZigBee feature called fragmentation that allows a single large data packet to be broken up into multiple
RF transmissions and reassembled by the receiver before sending data out its UART. This is shown in the
image below.
The API transmit frame can include up to 255 bytes of data, which will be broken up into multiple
transmissions and reassembled on the receiving side. If one or more of the fragmented messages are not
received by the receiving device, the receiver will drop the entire message, and the sender will indicate a
transmission failure in the Tx Status API frame. ZB firmware can only support one fragmented packet at a
time at the receive node, due to memory constraints.
Applications that do not wish to use fragmentation should avoid sending more than the maximum number
of bytes in a single RF transmission. See the "Maximum RF Payload Size" section for details.
Devices will not receive or reassemble fragmented RF packets if RTS flow control is enabled (D6 command).
Data Transmission Examples
AT Firmware
To send a da ta packet in AT firmware, the DH and DL commands must be se t to match the 64-b it address of
the destination device. DH must match the upper 4-bytes, and DL must match the lower 4 bytes. Since the
coordinator always receives a 16-bit address of 0x0000, a 64-bit address of 0x0000000000000000 is
defined as the coordinator's address (in ZB firmware). The default values of DH and DL are 0x00, which
sends data to the coordinator.
Example 1: Send a transmission to the coordinator.
(In this example, a '\r' refers to a carriage return character.)
A router or end device can send data in two ways. First, set the destination address (DH and DL
commands) to 0x00.
1. Enter command mode ('+++')
2. After receiving an OK\r, issue the following commands:
a. ATDH0\r
b. ATDL0\r
c. ATCN\r
3. Verify that each of the 3 commands returned an OK\r response.
4. After setting these command values, all serial characters will be sent as a unicast transmission
to the coordinator.
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Alternatively, if the coordinator's 64-bit address is known, DH and DL can be set to the coordinator's 64-bit
address. Suppose the coordinator's address is 0x0013A200404A2244.
1. Enter command mode ('+++')
2. After receiving an OK\r, issue the following commands:
a. ATDH13A200\r
b. ATDL404A2244\
c. ATCN\r
3. Verify that each of the 3 commands returned an OK\r response.
4. After setting these command values, all serial characters will be sent as a unicast transmission
to the coordinator.
API Firmware
Use the transmit request, or explicit transmit request frame (0x10 and 0x11 respectively) to send data to
the coordinator. The 64-bit address can either be set to 0x0000000000000000, or to the 64-bit address of
the coordinator. The 16-bit address should be set to 0xFFFE when using the 64-bit address of all 0x00s.
To send an ascii "1" to the coordinator's 0x00 address, the following API frame can be used:
7E 00 0F 10 01 0000 0000 0000 0000 FFFE 00 00 31 C0
If the explicit transmit frame is used, the cluster ID should be set to 0x0011, the profile ID to 0xC105, and
the source and destination endpoints to 0xE8 (recommended defaults for data transmissions in the Digi
profile.) The same transmission could be sent using the following explicit transmit frame:
7E 00 15 11 01 0000 0000 0000 0000 FFFE E8 E8 0011 C105 00 00 31 18
Notice the 16-bit address is set to 0xFFFE. This is required when sending to a 64-bit address of 0x00s.
Now suppose the coordinator's 64-bit address is 0x0013A200404A2244. The following transmit request API
frame (0x10) will send an ASCII "1" to the coordinator:
7E 00 0F 10 01 0013 A200 404A 2244 0000 0000 31 18
Example 2: Send a broadcast transmission.
(In this example, a '\r' refers to a carriage return character.)
Perform the following steps to configure a broadcast transmission:
1. Enter command mode ('+++')
2. After receiving an OK\r, issue the following commands:
a. ATDH0\r
b. ATDLffff\r
c. ATCN\r
3. Verify that each of the 3 commands returned an OK\r response
4. After setting these command values, all serial characters will be sent as a broadcast
transmission.
API Firmware
This example will use the transmit request API frame (0x10) to send an ASCII "1" in a broadcast
transmission.
To send an ascii "1" as a broadcast transmission, the following API frame can be used:
7E 00 0F 10 01 0000 0000 0000 FFFF FFFE 00 00 31 C2
Notice the destination 16-bit address is set to 0xFFFE for broadcast transmissions.
RF Packet Routing
Unicast transmissions may require some type of routing. ZigBee includes several different ways to route data, each
with its own advantages and disadvantages. These are summarized in the table below.
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Routing Approach Description When to Use
Ad hoc On-demand
Distance Vector (AODV)
Mesh Routing
Routing paths are created between source and
destination, possibly traversing multiple nodes
(“hops”). Each device knows who to send data
to next to eventually reach the destination
Use in networks that will not scale beyond about
40 destination devices.
Many-to-One Routing A single broadcast transmission configures
Source Routing Data packets include the entire route the packet
Note – End devices do not make use of these routing protocols. Rather, an end device sends a unicast transmission to its
parent and allows the parent to route the data packet in its behalf.
Note - A network cannot revert from Many-to-One routing to AODV routing without first doing a network reset (NR).
reverse routes on all devices into the device that
sends the broadcast
should traverse to get from source to
destination
Useful when many remote devices send data to
a single gateway or collector device.
Improves routing efficiency in large networks
(over 40 remote devices)
Link Status Transmission
Before discussing the various routing protocols, it is worth understanding the primary mechanism in ZigBee for
establishing reliable bi-directional links. This mechanism is especially useful in networks that may have a
mixture of devices with varying output power and/or receiver sensitivity levels.
Each coordinator or router device periodically sends a link status message. This message is sent as a 1-hop
broadcast transmission, received only by one-hop neighbors. The link status message contains a list of
neighboring devices and incoming and outgoing link qualities for each neighbor. Using these messages,
neighboring devices can determine the quality of a bi-directional link with each neighbor and use that
information to select a route that works well in both directions.
For example, consider a network of two neighboring devices that send periodic link status messages. Suppose
that the output power of device A is +18dBm, and the output power of device B is +3dBm (considerably less
than the output power of device A). The link status messages might indicate the following:
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This mechanism enables devices A and B to recognize that the link is not reliable in both directions and select a
different neighbor when establishing routes. (Such links are called asymmetric links, meaning the link quality is
not similar in both directions.)
When a router or coordinator device powers on, it sends link status messages every couple seconds to attempt
to discover link qualities with its neighbors quickly. After being powered on for some time, the link status
messages are sent at a much slower rate (about every 3-4 times per minute).
AODV Mesh Routing
ZigBee employs mesh routing to establish a route between the source device and the destination. Mesh routing
allows data packets to traverse multiple nodes (hops) in a network to route data from a source to a destination.
Routers and coordinators can participate in establishing routes between source and destination devices using a
process called route discovery. The Route discovery process is based on the AODV (Ad-hoc On-demand Distance
Vector routing) protocol.
SampleTransmissionThroughaMeshNetwork
AODV (Ad-hoc On-demand Distance Vector) Routing Algorithm
Routing under the AODV protocol is accomplished using tables in each node that store the next hop
(intermediary node between source and destination nodes) for a destination node. If a next hop is not known,
route discovery must take place in order to find a path. Since only a limited number of routes can be stored on
a Router, route discovery will take place more often on a large network with communication between many
different nodes.
Node Destination Address Next Hop Address
R3
C
R5
When a source node must discover a route to a destination node, it sends a broadcast route request command.
The route request command contains the source network address, the destination network address and a path
cost field (a metric for measuring route quality). As the route request command is propagated through the
Router 6 Coordinator
Router 6 Router 5
Router 6 Router 6
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network (refer to the Broadcast Transmission), each node that re-broadcasts the message updates the path
cost field and creates a temporary entry in its route discovery table.
SampleRouteRequest(Broadcast)TransmissionWhereR3isTryi n g toDiscoveraRoutetoR6
When the destination node receives a route request, it compares the ‘path cost’ field against previously received
route request commands. If the path cost stored in the route request is better than any previously received, the
destination node will transmit a route reply packet to the node that originated the route request. Intermediate
nodes receive and forward the route reply packet to the source node (the node that originated route request).
SampleRouteReply(Unicast)WhereR6SendsaRouteReplytoR3.
Note: R6 could send multiple replies if it identifies a better route.
Retries and Acknowledgments
ZigBee includes acknowledgment packets at both the Mac and Application Support (APS) layers. When data is
transmitted to a remote device, it may traverse multiple hops to reach the destination. As data is transmitted
from one node to its neighbor, an acknowledgment packet (Ack) is transmitted in the opposite direction to
indicate that the transmission was successfully received. If the Ack is not received, the transmitting device will
retransmit the data, up to 4 times. This Ack is called the Mac layer acknowledgment.
In addition, the device that originated the transmission expects to receive an acknowledgment packet (Ack)
from the destination device. This Ack will traverse the same path that the data traversed, but in the opposite
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direction. If the originator fails to receive this Ack, it will retransmit the data, up to 2 times until an Ack is
received. This Ack is called the ZigBee APS layer acknowledgment.
Refer to the ZigBee specification for more details.
Many-to-One Routing
In networks where many devices must send data to a central collector or gateway device, AODV mesh routing
requires significant overhead. If every device in the network had to discover a route before it could send data to
the data collector, the network could easily become inundated with broadcast route discovery messages.
Many-to-one routing is an optimization for these kinds of networks. Rather than require each device to do its
own route discovery, a single many-to-one broadcast transmission is sent from the data collector to establish
reverse routes on all devices. This is shown in the figure below. The left side shows the many broadcasts the
devices can send when they create their own routes and the route replies generated by the data collector. The
right side shows the benefits of many-to-one routing where a single broadcast creates reverse routes to the
data collector on all routers.
The many-to-one broadcast is a route request message with the target discovery address set to the address of
the data collector. Devices that receive this route request create a reverse many-to-one routing table entry to
create a path back to the data collector. The ZigBee stack on a device uses historical link quality information
about each neighbor to select a reliable neighbor for the reverse route.
When a device sends data to a data collector, and it finds a many-to-one route in its routing table, it will
transmit the data without performing a route discovery. The many-to-one route request should be sent
periodically to update and refresh the reverse routes in the network.
Applications that require multiple data collectors can also use many-to-one routing. If more than one data
collector device sends a many-to-one broadcast, devices will create one reverse routing table entry for each
collector.
In ZB firmware, the AR command is used to enable many-to-one broadcasting on a device. The AR command
sets a time interval (measured in 10 second units) for sending the many to one broadcast transmission. (See
the command table for details.)
Source Routing
In applications where a device must transmit data to many remotes, AODV routing would require performing
one route discovery for each destination device to establish a route. If there are more destination devices than
there are routing table entries, established AODV routes would be overwritten with new routes, causing route
discoveries to occur more regularly. This could result in larger packet delays and poor network performance.
ZigBee source routing helps solve these problems. In contrast to many-to-one routing that establishes routing
paths from many devices to one data collector, source routing allows the collector to store and specify routes for
many remotes.
To use source routing, a device must use the API firmware, and it must send periodic many-to-one route
request broadcasts (AR command) to create a many-to-one route to it on all devices. When remote devices
send RF data using a many-to-one route, they first send a route record transmission. The route record
transmission is unicast along the many-to-one route until it reaches the data collector. As the route record
traverses the many-to-one route, it appends the 16-bit address of each device in the route into the RF payload.
When the route record reaches the data collector, it contains the address of the sender, and the 16-bit address
of each hop in the route. The data collector can store the routing information and retrieve it later to send a
source routed packet to the remote. This is shown in the images below.
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The data collector sends a
Many-to-One route request
broadcast to create reverse
routes on all devices.
A remote device sends an RF data packet
to the data collector. (This is prefaced by
a route record transmission to the data
collector.)
Acquiring Source Routes
Acquiring source routes requires the remote devices to send a unicast to a data collector (device that sends
many-to-one route request broadcasts). There are several ways to force remotes to send route record
transmissions.
After obtaining a source route, the data
collector sends a source routed
transmission to the remote device.
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1. If the application on remote devices periodically sends data to the data collector, each
transmission will force a route record to occur.
2. The data collector can issue a network discovery command (ND command) to force all XBee
devices to send a network discovery response. Each network discovery response will be prefaced by a route
record.
3. Periodic IO sampling can be enabled on remotes to force them to send data at a regular rate.
Each IO sample would be prefaced by a route record. (See chapter 8 for details.)
4. If the NI string of the remote device is known, the DN command can be issued with the NI
string of the remote in the payload. The remote device with a matc hing NI string would send a route record
and a DN response.
Storing Source Routes
When a data collector receives a route record, it sends it out the UART as a Route Record Indicator API
frame (0xA1). To use source routing, the application should receive these frames and store the source
route information.
Sending a Source Routed Transmission
To send a source routed transmission, the application should send a Create Source Route API frame (0x21)
to the XBee to create a source route in its internal source route table. After sending the Create Source
Route API frame, the application can send data transmission or remote command request frames as needed
to the same destination, or any destination in the source route. Once data must be sent to a new
destination (a destination not included in the last source route), the application should first send a new
Create Source Route API frame. The XBee can buffer one source route that includes up to 10 hops
(excluding source and destination).
For example, suppose a network exists with a coordinator and 5 routers (R1, R2, R3, R4, R5) with known
source routes as shown below.
To send a source-routed packet to R3, the application must send a Create Source Route API frame (0x21)
to the XBee, with a destination of R3, and 2 hops (R1 and R2). If the 64- bit address of R3 is 0x0013A200
404a1234 and the 16-bit addresses of R1, R2, and R3 are:
Device 16-bit address
R1 0xAABB
R2 0xCCDD
R3 0xEEFF
Then the Create Source Route API frame would be:
7E 0012 21 00 0013A200 404A1234 EEFF 00 02 CCDD AABB 5C
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Where:
0x0012 - length
0x21 - API ID (create source route)
0x00 - frame ID (set to 0 always)
0x0013A200 404A1234 - 64-bit address of R3 (destination)
0xEEFF - 16-bit address of R3 (destination)
0x00 - Route options (set to 0)
0x02 - Number of intermediate devices in the source route
0xCCDD - Address of furthest device (1-hop from target)
0xAABB - Address of next-closer device
0x5C - Checksum (0xFF - SUM (all bytes after length))
Repairing Source Routes
It is possible in a network to have an existing source route fail (i.e. a device in the route moves or goes
down, etc.). If a device goes down in a source routed network, all routes that used the device will be
broken.
As mentioned previously, source routing must be used with many-to-one routing. (A device that uses
source routing must also send a periodic many-to-one broadcast in order to keep routes fresh). If a source
route is broken, remote devices must send in new route record transmissions to the data collector to
provide it with a new source route. This requires that remote devices periodically send data transmissions
into the data collector. See the earlier "Acquiring Source Routes" section for details.
Retries and Acknowledgments
ZigBee includes acknowledgment packets at both the Mac and Application Support (APS) layers. When data
is transmitted to a remote device, it may traverse multiple hops to reach the destination. As data is
transmitted from one node to its neighbor, an acknowledgment packet (Ack) is transmitted in the opposite
direction to indicate that the transmission was successfully received. If the Ack is not received, the
transmitting device will retransmit the data, up to 4 times. This Ack is called the Mac layer
acknowledgment.
In addition, the device that originated the transmission expects to receive an acknowledgment packet (Ack)
from the destination device. This Ack will traverse the same path that the data traversed, but in the
opposite direction. If the originator fails to receive this Ack, it will retransmit the data, up to 2 times until an
Ack is received. This Ack is called the ZigBee APS layer acknowledgment.
Refer to the ZigBee specification for more details.
Encrypted Transmissions
Encrypted transmissions are routed similar to non-encrypted transmissions with one exception. As an encrypted
packet propagates from one device to another, each device decrypts the packet using the network key, and
authenticates the packet by verifying packet integrity. It then re-encrypts the packet with its own source address
and frame counter values, and sends the message to the next hop. This process adds some overhead latency to
unicast transmissions, but it helps prevent replay attacks. See chapter 5 for details.
Maximum RF Payload Size
XBee ZB firmware includes a command (ATNP) that returns the maximum number of RF payload bytes that can be
sent in a unicast transmission. Querying the NP command, like most other commands, returns a HEXADECIMAL
value. This number will change based on whether security is enabled or not. If security is enabled (EE command),
the maximum number of RF payload bytes decreases since security requires additional overhead.
After reading the NP value, the following conditions can affect the maximum number of data bytes in a single RF
transmission:
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•Broadcast transmissions can support 8 bytes more than unicast transmissions.
•If source routing is used, the 16-bit addresses in the source route are inserted into the RF payload space. For
example, if NP returns 84 bytes, and a source route must traverse 3 intermediate hops (3 16-bit addresses),
the total number of bytes that can be sent in one RF packet is 78.
•Enabling APS encryption (API tx option bit set) will reduce the number of payload bytes by 4.
Throughput
Throughput in a ZigBee network can vary by a number of variables, including: number of hops, encryption enabled/
disabled, sleeping end devices, failures/route discoveries. Our empirical testing showed the following throughput
performance in a robust operating environment (low interference).
Data Throughput*
Configuration Data Throughput
1 hop, RR, SD 35kbps
1 hop, RR, SE 19kbps
1 hop, RE, SD 25kbps
1 hop, RE, SE 16kbps
1 hop, ER, SD 21kbps
1 hop, ER, SE 16kbps
4 hops, RR, SD 10kbps
4 hops, RR, SE 5kbps
RR = router to router,
RE = router to end device (non-sleeping),
ER = end device (non-sleeping) to router,
SD = security disabled,
SE = security enabled.
4 hops = 5 nodes total, 3 intermediate router nodes
* Data throughput measurements were made setting the serial interface rate to 115200 bps, and measuring the
time to send 100,000 bytes from source to destination. During the test, no route discoveries or failures occurred.
ZDO Transmissions
ZigBee defines a ZigBee Device Objects layer (ZDO) that can provide device and service discovery and network
management capabilities. This layer is described below.
ZigBee Device Objects (ZDO)
The ZigBee Device Objects (ZDO) is supported to some extent on all ZigBee devices. The ZDO is an endpoint
that implements services described in the ZigBee Device Profile in the ZigBee specification. Each service has an
assigned cluster ID, and most service requests have an associated response. The following table describes some
common ZDO services.
Cluster Name Cluster ID Description
Network Address
Request
Active Endpoints
Request
0x0000 Request a 16-bit address of the
0x0005 Request a list of endpoints from a
radio with a matching 64-bit
address (required parameter).
remote device.
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LQI Request 0x0031 Request data from a neighbor table
Routing Table
Request
Network Address
Response
Cluster Name Cluster ID Description
LQI Response 0x8031 Response that includes neighbor
Routing Table
Response
Refer to the ZigBee specification for a detailed description of all ZigBee Device Profile services.
0x0032 Request to retrieve routing table
0x8000 Response that includes the 16-bit
0x8032 Response that includes routing
of a remote device.
entries from a remote device.
address of a device.
table data from a remote device.
table entry data from a remote
device.
Sending a ZDO Command
To send a ZDO command, an explicit transmit API frame must be used and formatted correctly. The source and
destination endpoints must be set to 0, and the profile ID must be set to 0. The cluster ID must be set to match
the cluster ID of the appropriate service. For example, to send an active endpoints request, the cluster ID must
be set to 0x0005.
The first byte of payload in the API frame is an application sequence number (transaction sequence number)
that can be set to any single byte value. This same value will be used in the first byte of the ZDO response. All
remaining payload bytes must be set as required by the ZDO. All multi-byte values must be sent in little endian
byte order.
Receiving ZDO Commands and Responses
In XBee ZB firmware, ZDO commands can easily be sent using the API. In order to receive incoming ZDO
commands, receiver application addressing must be enabled with the AO command. (See examples later in this
section.) Not all incoming ZDO commands are passed up to the application.
When a ZDO message is received on endpoint 0 and profile ID 0, the cluster ID indicates the type of ZDO
message that was received. The first byte of payload is generally a sequence number that corresponds to a
sequence number of a request. The remaining bytes are set as defined by the ZDO. Similar to a ZDO request,
all multi-byte values in the response are in little endian byte order.
Example 1: Send a ZDO LQI Request to read the neighbor table contents of a remote.
Looking at the ZigBee specification, the cluster ID for an LQI Request is 0x0031, and the payload only
requires a single byte (start index). This example will send an LQI request to a remote device with a 64-bit
address of 0x0013A200 40401234. The start index will be set to 0, and the transaction sequence number
will be set to 0x76
API Frame:
7E 0016 11 01 0013A200 40401234 FFFE 00 00 0031 0000 00 00 76 00 CE
0x0016 - length
0x11 - Explicit transmit request
0x01 - frame ID (set to a non-zero value to enable the transmit status message, or set to 0 to disable)
0x0013A200 40401234 - 64-bit address of the remote
0xFFFE - 16-bit address of the remote (0xFFFE = unknown). Optionally, set to the 16-bit address of the
destination if known.
0x00 - Source endpoint
0x00 - Destination endpoint
0x0031 - Cluster ID (LQI Request, or Neighbor table request)
0x0000 - Profile ID (ZigBee Device Profile)
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0x00 - Broadcast radius
0x00 - Tx Options
0x76 - Transaction sequence number
0x00 - Required payload for LQI request command
0xCE - Checksum (0xFF - SUM (all bytes after length))
Description:
This API frame sends a ZDO LQI request (neighbor table request) to a remote device to obtain data from it s
neighbor table. Recall that the AO command must be set correctly on an API device to enable the explicit
API receive frames in order to receive the ZDO response.
Example 2: Send a ZDO Network Address Request to discover the 16-bit address of a remote.
Looking at the ZigBee specification, the cluster ID for a network Address Request is 0x0000, and the
payload only requires the following:
[64-bit address] + [Request Type] + [Start Index]
This example will send a Network Address Request as a broadcast transmission to discover the 16-bit
address of the device with a 64-bit address of 0x0013A200 40401234. The request type and start index will
be set to 0, and the transaction sequence number will be set to 0x44
API Frame:
7E 001F 11 01 00000000 0000FFFF FFFE 00 00 0000 0000 00 00 44 34124040 00A21300 00 00 33
0x001F - length
0x11 - Explicit transmit request
0x01 - frame ID (set to a non-zero value to enable the transmit status message, or set to 0 to disable)
0x00000000 0000FFFF - 64-bit address for a broadcast transmission
0xFFFE - Set to this value for a broadcast transmission.
0x00 - Source endpoint
0x00 - Destination endpoint
0x0000 - Cluster ID (Network Address Request)
0x0000 - Profile ID (ZigBee Device Profile)
0x00 - Broadcast radius
0x00 - Tx Options
0x44 - Transaction sequence number
0x34124040 00A21300 00 00 - Required payload for Network Address Request command
0x33 - Checksum (0xFF - SUM (all bytes after length))
Description:
This API frame sends a broadcast ZDO Network Address Request to obtain the 16-bit address of a device
with a 64-bit address of 0x0013A200 40401234. Note the bytes for the 64-bit address were inserted in
little endian byte order. All multi-byte fields in the API payload of a ZDO command must have their data
inserted in little endian byte order. Also recall that the AO command must be set correctly on an API device
to enable the explicit API receive frames in order to receive the ZDO response.
Transmission Timeouts
The ZigBee stack includes two kinds of transmission timeouts, depending on the nature of the destination device.
For destination devices such as routers whose receiver is always on, a unicast timeout is used. The unicast timeout
estimates a timeout based on the number of unicast hops the packet should traverse to get data to the destination
device. For transmissions destined for end devices, the ZigBee stack uses an extended timeout that includes the
unicast timeout (to route data to the end device's parent), and it includes a timeout for the end device to finish
sleeping, wake, and poll the parent for data.
The ZigBee stack includes some provisions for a device to detect if the destination is an end device or not. The
ZigBee stack uses the unicast timeout unless it knows the destination is an end device.
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The XBee API includes a transmit options bit that can be set to specify if the extended timeout should be used for a
given transmission. If this bit is set, the extended timeout will be used when sending RF data to the specified
destination. To improve routing reliability, applications should set the extended timeout bit when sending data to end
devices if:
•The application sends data to 10 or more remote devices, some of which are end devices, AND
•The end devices may sleep longer than the unicast timeout
Equations for these timeouts are computed in the following sections.
Note: The timeouts in this section are worst-case timeouts and should be padded by a few hundred milliseconds.
These worst-case timeouts apply when an existing route breaks down (e.g. intermediate hop or destination device
moved).
Unicast Timeout
The unicast timeout is settable with the NH command. The actual unicast timeout is computed as ((50 * NH) +
100). The default NH value is 30 which equates to a 1.6 second timeout.
The unicast timeout includes 3 transmission attempts (1 attempt and 2 retries). The maximum total timeout is
about:
3 * ((50 * NH) + 100).
For example, if NH=30 (0x1E), the unicast timeout is about
3 * ((50 * 30) + 100), or
3 * (1500 + 100), or
3 * (1600), or
4800 ms, or
4.8 seconds.
Extended Timeout
The worst-case transmission timeout when sending data to an end device is somewhat larger than when
transmitting to a router or coordinator. As described later in chapter 6, RF data packets are actually sent to the
parent of the end device, who buffers the packet until the end device wakes to receive it. The parent will buffer
an RF data packet for up to (1.2 * SP) time.
To ensure the end device has adequate time to wake and receive the data, the extended transmission timeout
to an end device is:
(50 * NH) + (1.2 * SP)
This timeout includes the packet buffering timeout (1.2 * SP) and time to account for routing through the mesh
network (50 * NH).
If an acknowledgment is not received within this time, the sender will resend the transmission up to two more
times. With retries included, the longest transmission timeout when sending data to an end device is:
3 * ((50 * NH) + (1.2 * SP))
The SP value in both equations must be entered in millisecond units. (The SP command setting uses 10ms units
and must be converted to milliseconds to be used in this equation.)
For example, suppose a router is configured with NH=30 (0x1E) and SP=0x3E8 (10,000 ms), and that it is
either trying to send data to one of its end device children, or to a remote end device. The total extended
timeout to the end device is about:
3 * ((50 * NH) + (1.2 * SP)), or
3 * (1500 + 12000), or
3 * (13500), or
40500 ms, or
40.5 seconds.
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Transmission Examples
Example 1: Send a unicast API data transmission to the coordinator using 64-bit address 0, with
payload "TxData".
API Frame:
7E 0014 10 01 00000000 00000000 FFFE 00 00 54 78 44 61 74 61 AB
Field Composition:
0x0014 - length
0x10 - API ID (tx data)
0x01 - frame ID (set greater than 0 to enable the tx-status response)
0x00000000 00000000 - 64-bit address of coordinator (ZB definition)
0xFFFE - Required 16-bit address if sending data to 64-bit address of 0.
0x00 - Broadcast radius (0 = max hops)
0x00 - Tx options
0x54 78 44 61 74 61 - ASCII representation of "TxData" string
0xAB - Checksum (0xFF - SUM (all bytes after length))
Description:
This transmission sends the string "TxData" to the coordinator, without knowing the coordinator device's 64-bit
address. A 64-bit address of 0 is defined as the coordinator in ZB firmware. If the coordinator's 64-bit address
was known, the 64-bit address of 0 could be replaced with the coordinator's 64-bit address, and the 16-bit
address could be set to 0.
Example 2 - Send a broadcast API data transmission that all devices can receive (including sleeping
end devices), with payload "TxData".
API Frame:
7E 0014 10 01 00000000 0000FFFF FFFE 00 00 54 78 44 61 74 61 AD
Field Composition:
0x0014 - length
0x10 - API ID (tx data)
0x01 - frame ID (set to a non-zero value to enable the tx-status response)
0x00000000 0000FFFF - Broadcast definition (including sleeping end devices
0xFFFE - Required 16-bit address to send broadcast transmission.
0x00 - Broadcast radius (0 = max hops)
0x00 - Tx options
0x54 78 44 61 74 61 - ASCII representation of "TxData" string
0xAD - Checksum (0xFF - SUM (all bytes after length))
Description:
This transmission sends the string "TxData" as a broadcast transmission. Since the destination address is set to
0xFFFF, all devices, including sleeping end devices can receive this broadcast.
If receiver application addressing is enabled, the XBee will report all received data frames in the explicit format
(0x91) to indicate the source and destination endpoints, cluster ID, and profile ID that each packet was received
on. (Status messages like modem status and route record indicators are not affected.)
To enable receiver application addressing, set the AO command to 1 using the AT command frame (0x08).
Here's how to do this:
API Frame:
7E 0005 08 01 414F 01 65
Field Composition:
0x0005 - length
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0x08 - API ID (at command)
0x01 - frame ID (set to a non-zero value to enable AT command response frames)
0x414F - ASCII representation of 'A','O' (the command being issued)
0x01 - Parameter value
0x65 - Checksum (0xFF - SUM (all bytes after length))
Description:
Setting AO=1 is required for the XBee to use the explicit receive API frame (0x91) when RF data packets are
received. This is required if the application needs indication of source or destination endpoint, cluster ID, and/
or profile ID values used in received ZigBee data packets. ZDO messages can only be received if AO=1.
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5.Security
ZigBee supports various levels of security that can be configured depending on the needs of the application. Security
provisions include:
•128-bit AES encryption
•Two security keys that can be preconfigured or obtained during joining
•Support for a trust center
•Provisions to ensure message integrity, confidentiality, and authentication.
The first half of this chapter describes various security features defined in the ZigBee-PRO specification, while the last
half illustrates how the XBee and XBee-PRO modules can be configured to support these features
Security Modes
The ZigBee standard supports three security modes – residential, standard, and high security. Residential security
was first supported in the ZigBee 2006 standard. This level of security requires a network key be shared among
devices. Standard security adds a number of optional security enhancements over residential security, including an
APS layer link key. High security adds entity authentication, and a number of other features not widely supported.
XBee ZB modules primarily support standard security, although end devices that support residential security can join
and interoperate with standard security devices. The remainder of this chapter focuses on material that is relevant
to standard security.
ZigBee Security Model
ZigBee security is applied to the Network and APS layers. Packets are encrypted with 128-bit AES encryption. A
network key and optional link key can be used to encrypt data. Only devices with the same keys are able to
communicate together in a network. Routers and end devices that will communicate on a secure network must
obtain the correct security keys.
Network Layer Security
The network key is used to encrypt the APS layer and application data. In addition to encrypting application
messages, network security is also applied to route request and reply messages, APS commands, and ZDO
commands. Network encryption is not applied to MAC layer transmissions such as beacon transmissions, etc. If
security is enabled in a network, all data packets will be encrypted with the network key.
Packets are encrypted and authenticated using 128-bit AES. This is shown in the figure below.
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Frame Counter
The network header of encrypted packets includes a 32-bit frame counter. Each device in the network maintains
a 32-bit frame counter that is incremented for every transmission. In addition, devices track the last known 32bit frame counter for each of its neighbors. If a device receives a packet from a neighbor with a smaller frame
counter than it has previously seen, the packet is discarded. The frame counter is used to protect against replay
attacks.
If the frame counter reaches a maximum value of 0xFFFFFFFF, it does not wrap to 0 and no more transmissions
can be sent. Due to the size of the frame counters, reaching the maximum value is a very unlikely event for
most applications. The following table shows the required time under different conditions, for the frame counter
to reach its maximum value.
Average Transmission Rate Time until 32-bit frame counter expires
1 / second 136 years
10 / second 13.6 years
To clear the frame counters without compromising security, the network key can be changed in the network.
When the network key is updated, the frame counters on all devices reset to 0. (See the Network Key Updates
section for details.)
Message Integrity Code
The network header, APS header, and application data are all authenticated with 128-bit AES. A hash is
performed on these fields and is appended as a 4-byte message integrity code (MIC) to the end of the packet.
The MIC allows receiving devices to ensure the message has not been changed. The MIC provides message
integrity in the ZigBee security model. If a device receives a packet and the MIC does not match the device’s
own hash of the data, the packet is dropped.
Network Layer Encryption and Decryption
Packets with network layer encryption are encrypted and decrypted by each hop in a route. When a device
receives a packet with network encryption, it decrypts the packet and authenticates the packet. If the device is
not the destination, it then encrypts and authenticates the packet, using its own frame counter and source
address in the network header section.
Since network encryption is performed at each hop, packet latency is slightly longer in an encrypted network
than in a non-encrypted network. Also, security requires 18 bytes of overhead to include a 32-bit frame counter,
an 8-byte source address, 4-byte MIC, and 2 other bytes. This reduces the number of payload bytes that can be
sent in a data packet.
Network Key Updates
ZigBee supports a mechanism for changing the network key in a network. When the network key is changed,
the frame counters in all devices reset to 0.
APS Layer Security
APS layer security can be used to encrypt application data using a key that is shared between source and
destination devices. Where network layer security is applied to all data transmissions and is decrypted and reencrypted on a hop-by-hop basis, APS security is optional and provides end-to-end security using an APS link
key that only the source and destination device know. APS security can be applied on a packet-by-packet basis.
APS security cannot be applied to broadcast transmissions.
If APS security is enabled, packets are encrypted and authenticated using 128-bit AES. This is shown in the
figure below:
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Message integrity Code
If APS security is enabled, the APS header and data payload are authenticated with 128-bit AES. A hash is
performed on these fields and appended as a 4-byte message integrity code (MIC) to the end of the packet.
This MIC is different than the MIC appended by the network layer. The MIC allows the destination device to
ensure the message has not been changed. If the destination device receives a packet and the MIC does not
match the destination device’s own hash of the data, the packet is dropped.
APS Link Keys
There are two kinds of APS link keys – trust center link keys and application link keys. A trust center link key is
established between a device and the trust center, where an application link key is established between a device
and another device in the network where neither device is the trust center.
APS Layer Encryption and Decryption
Packets with APS layer encryption are encrypted at the source and only decrypted by the destination. Since APS
encryption requires a 5-byte header and a 4-byte MIC, the maximum data payload is reduced by 9 bytes when
APS encryption is used.
Network and APS Layer Encryption
Network and APS layer encryption can both be applied to data. The following figure demonstrates the
authentication and encryption performed on the final ZigBee packet when both are applied.
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Trust Center
ZigBee defines a trust center device that is responsible for authenticating devices that join the network. The
trust center also manages link key distribution in the network.
Forming and Joining a Secure Network
The coordinator is responsible for selecting a network encryption key. This key can either be preconfigured or
randomly selected. In addition, the coordinator generally operates as a trust center and must therefore select
the trust center link key. The trust center link key can also be preconfigured or randomly selected.
Devices that join the network must obtain the network key when they join. When a device joins a secure
network, the network and link keys can be sent to the joining device. If the joining device has a pre-configured
trust center link key, the network key will be sent to the joining device encrypted by the link key. Otherwise, if
the joining device is not pre-configured with the link key, the device could only join the network if the network
key is sent unencrypted (“in the clear”). The trust center must decide whether or not to send the network key
unencrypted to joining devices that are not pre-configured with the link key. Sending the network key
unencrypted is not recommended as it can open a security hole in the network. To maximize security, devices
should be pre-configured with the correct link key.
Implementing Security on the XBee
If security is enabled in the XBee ZB firmware, devices acquire the network key when they join a network. Data
transmissions are always encrypted with the network key, and can optionally be end-to-end encrypted with the APS
link key. The following sections discuss the security settings and options in the XBee ZB firmware.
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Enabling Security
To enable security on a device, the EE command must be set to 1. If the EE command value is changed and
changes are applied (e.g. AC command), the XBee module will leave the network (PAN ID and channel) it was
operating on, and attempt to form or join a new network.
If EE is set to 1, all data transmissions will be encrypted with the network key. When security is enabled, the
maximum number of bytes in a single RF transmission will be reduced. See the NP command for details.
Note: The EE command must be set the same on all devices in a network. Changes to the EE command should
be written to non-volatile memory (to be preserved through power cycle or reset events) using the WR
command.
Setting the Network Security Key
The coordinator must select the network security key for the network. The NK command (write-only) is used to
set the network key. If NK=0 (default), a random network key will be selected. (This should suffice for most
applications.) Otherwise, if NK is set to a non-zero value, the network security key will use the value specified
by NK. NK is only supported on the coordinator.
Routers and end devices with security enabled (ATEE=1) acquire the network key when they join a network.
They will receive the network key encrypted with the link key if they share a pre-configured link key with the
coordinator. See the following section for details.
Setting the APS Trust Center Link Key
The coordinator must also select the trust center link key, using the KY command. If KY=0 (default), the
coordinator will sel ect a rand om trust center link key (not recommended) . O therwise, if KY is se t g reater than 0,
this value will be used as the pre-configured trust center link key. KY is write-only and cannot be read.
Note: Application link keys (sent between two devices where neither device is the coordinator) are not
supported in ZB firmware at this time.
Random Trust Center Link Keys
If the coordinator selects a random trust center link key (KY=0, default), then it will allow devices to join
the network without having a pre-configured link key. However, this will cause the network key to be sent
unencrypted over-the-air to joining devices and is not recommended.
Pre-configured Trust Center Link Keys
If the coordinator uses a pre-configured link key (KY > 0), then the coordinator will not send the network
key unencrypted to joining devices. Only devices with the correct pre-configured link key will be able to join
and communicate on the network.
Enabling APS Encryption
APS encryption is an optional layer of security that uses the link key to encrypt the data payload. Unlike network
encryption that is decrypted and encrypted on a hop-by-hop basis, APS encryption is only decrypted by the
destination device. The XBee must be configured with security enabled (EE set to 1) to use APS encryption.
APS encryption can be enabled in API firmware on a per-packet basis. To enable APS encryption for a given
transmission, the "enable APS encryption" transmit options bit should be set in the API transmit frame. Enabling
APS encryption decreases the maximum payload size by 9 bytes.
Using a Trust Center
The EO command can be used to define the coordinator as a trust center. If the coordinator is a trust center, it
will be alerted to all new join attempts in the network. The trust center also has the ability to update or change
the network key on the network.
In ZB firmware, a secure network can be established with or without a trust center. Network and APS layer
encryption are supported if a trust center is used or not.
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Updating the Network Key with a Trust Center
If the trust center has started a network and the NK value is changed, the coordinator will update the
network key on all devices in the network. (Changes to NK will not force the device to leave the network.)
The network will continue to operate on the same channel and PAN ID, but the devices in the network will
update their network key, increment their network key sequence number, and restore their frame counters
to 0.
Updating the Network Key without a Trust Center
If the coordinator is not running as a trust center, the network reset command (NR1) can be used to force
all devices in the network to leave the current network and rejoin the network on another channel. When
devices leave and reform then network, the frame counters are reset to 0. This approach will cause the
coordinator to form a new network that the remaining devices should join. Resetting the network in this
manner will bring the coordinator and routers in the network down for about 10 seconds, and will likely
cause the 16-bit PAN ID and 16-bit addresses of the devices to change.
XBee Security Examples
This section covers some sample XBee configurations to support different security modes. Several AT commands are
listed with suggested parameter values. The notation in this section includes an '=' sign to indicate what each
command register should be set to - for example, EE=1. This is not the correct notation for setting command values
in the XBee. In AT command mode, each command is issued with a leading 'AT' and no '=' sign - for example ATEE1.
In the API, the two byte command is used in the command field, and parameters are populated as binary values in
the parameter field.
Example 1: Forming a network with security (pre-configured link keys)
1. Start a coordinator with the following settings:
a. ID=2234 (arbitrarily selected)
b. EE=1
c. NK=0
d. KY=4455
e. WR (save networking parameters to preserve them through power cycle)
2. Configure one or more routers or end devices with the following settings:
a. ID=2234
b. EE=1
c. KY=4455
d. WR (save networking parameters to preserve them through power cycle)
3. Read the AI setting on the coordinator and joining devices until they return 0 (formed or joined
a network).
In this example, EE, ID, and KY are set the same on all devices. After successfully joining the secure network,
all application data transmissions will be encrypted by the network key. Since NK was set to 0 on the
coordinator, a random network key was selected. And since the link key (KY) was configured the same on all
devices, to a non-zero value, the network key was sent encrypted by the pre-configured link key (KY) when the
devices joined.
Example 2: Forming a network with security (obtaining keys during joining)
1. Start a coordinator with the following settings:
a. ID=2235
b. EE=1
c. NK=0
d. KY=0
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e. WR (save networking parameters to preserve them through power cycle)
2. Configure one or more routers or end devices with the following settings:
a. ID=2235
b. EE=1
c. KY=0
d. WR (save networking parameters to preserve them through power cycle)
3. Read the AI setting on the coordinator and joining devices until they return 0 (formed or joined
a network).
In this example, EE, ID, and KY are set the same on all devices. Since NK was set to 0 on the coordinator, a
random network key was selected. And since KY was set to 0 on all devices, the network key was sent
unencrypted ("in the clear") when the devices joined. This approach introduces a security vulnerability into the
network and is not recommended.
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6.NetworkCommissioningandDiagnostics
Network commissioning is the process whereby devices in a mesh network are discovered and configured for operation.
The XBee modules include several features to support device discovery and configuration. In addition to configuring
devices, a strategy must be developed to place devices to ensure reliable routes.
To accommodate these requirements, the XBee modules include various features to aid in device placement,
configuration, and network diagnostics.
Device Configuration
XBee/XBee-PRO ZB modules can be configured locally through serial commands (AT or API), or remotely through
remote API commands. API devices can send configuration commands to set or read the configuration settings of
any device in the network.
Device Placement
For a mesh network installation to be successful, the installer must be able to determine where to place individual
XBee devices to establish reliable links throughout the mesh network.
Link Testing
A good way to measure the performance of a mesh network is to send unicast data through the network from
one device to another to determine the success rate of many transmissions. To simplify link testing, the
modules support a loopback cluster ID (0x12) on the data endpoint (0xE8). Any data sent to this cluster ID on
the data endpoint will be transmitted back to the sender. This is shown in the figure below:
The configuration steps to send data to the loopback cluster ID depend on the firmware type.
AT Firmware
To send data to the loopback cluster ID on the data endpoint of a remote device, set the CI command value to
0x12. The SE and DE commands should be set to 0xE8 (default valu e). The DH and DL commands should be set
to the address of the remote (0 for the coordinator, or the 64-bit address of the remote). After exiting command
mode, any received serial characters will be transmitted to the remote device, and returned to the sender.
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API Firmware
Send an Explicit Addressing ZigBee Command API frame (0x11) using 0x12 as the cluster ID and 0xE8 as the
source and destination endpoint. Data packets received by the remote will be echoed back to the sender.
RSSI Indicators
It is possible to measure the received signal strength on a device using the DB command. DB returns the RSSI
value (measured in –dBm) of the last received packet. However, this number can be misleading. The DB value
only indicates the received signal strength of the last hop. If a transmission spans multiple hops, the DB value
provides no indication of the overall transmission path, or the quality of the worst link – it only indicates the
quality of the last link and should be used sparingly.
The DB value can be determined in hardware using the RSSI/PWM module pin (pin 6). If the RSSI PWM
functionality is enabled (P0 command), when the module receives data, the RSSI PWM is set to a value based
on the RSSI of the received packet. (Again, this value only indicates the quality of the last hop.) This pin could
potentially be connected to an LED to indicate if the link is stable or not.
Device Discovery
Network Discovery
The network discovery command can be used to discover all Digi modules that have joined a network. Issuing
the ND command sends a broadcast node discovery command throughout the network. All devices that receive
the command will send a response that includes the device’s addressing information, node identifier string (see
NI command), and other relevant information. This command is useful for generating a list of all module
addresses in a network.
When a device receives the node discovery command, it waits a random time before sending its own response.
The maximum time delay is set on the ND sender with the NT command. The ND originator includes its NT
setting in the transmission to provide a delay window for all devices in the network. Large networks may need
to increase NT to improve network discovery reliability. The default NT value is 0x3C (6 seconds).
ZDO Discovery
The ZigBee Device Profile includes provisions to discover devices in a network that are supported on all ZigBee
devices (including non-Digi products). These include the LQI Request (cluster ID 0x0031) and the Network
Update Request (cluster ID 0x0038). The LQI Request can be used to read the devices in the neighbor table of
a remote device, and the Network Update Request can be used to have a remote device do an active scan to
discover all nearby ZigBee devices. Both of these ZDO commands can be sent using the XBee Explicit API
transmit frame (0x11). See the API chapter for details. Refer to the ZigBee specification for formatting details of
these two ZDO frames.
Joining Announce
All ZigBee devices send a ZDO Device Announce broadcast transmission when they join a ZigBee network (ZDO
cluster ID 0x0013). These frames will be sent out the XBee's UART as an Explicit Rx Indicator API frame (0x91)
if AO is set to 1. The device announce payload includes the following information:
[ Sequence Number] + [16-bit address] + [64-bit address] + [Capability]
The 16-bit and 64-bit addresses are received in little-endian byte order (LSB first). See the ZigBee specification
for details.
Commissioning Pushbutton and Associate LED
The XBee modules support a set of commissioning and LED behaviors to aid in device deployment and
commissioning. These include the commissioning pushbutton definitions and associate LED behaviors. These
features can be supported in hardware as shown below.
CommissioningPushbuttonandAssociateLEDFunctionalities
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XBee
20
15
Push button
R
Associate
LED
A pushbutton and an LED can be connected to module pins 20 and 15 respectively to
support the commissioning pushbutton and associate LED functionalities.
Commissioning Pushbutton
The commissioning pushbutton definitions provide a variety of simple functions to aid in deploying devices in a
network. The commissioning button functionality on pin 20 is enabled by setting the D0 command to 1 (enabled
by default).
If module is not joined to a net-
work
• Wakes an end device for
30 seconds
• Blinks a numeric error
code on the Associate pin
indicating the cause of
Presses
1
Button
If module is joined to a network
• Wakes an end device for
30 seconds
• Sends a node identification broadcast transmission
join failure (see section
6.4.2).
• Sends a broadcast trans-
•N/A
mission to enable joining
on the coordinator and all
devices in the network for
2
1 minute. (If joining is
permanently enabled on a
device (NJ = 0xFF), this
action has no effect on
that device.)
• Causes the device to leave
the PAN.
• Issues ATRE to restore
module parameters to
4
Button presses may be simulated in software using the ATCB command. ATCB should be issued with a
default values, including
ID and SC.
• The device attempts to
join a network based on
its ID and SC settings.
• Issues ATRE to restore
module parameters to
default values, including
ID and SC.
• The device attempts to
join a network based on
its ID and SC settings.
parameter set to the number of button presses to execute. (e.g. sending ATCB1 will execute the action(s)
associated with a single button press.)
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Δt
Device Not Joined
Dev ice has joined a netw ork
Associate
The associate pin can indicate the joined status of a device . Once the device has joined a
network, the associate pin toggles state at a regular interval (Δt). The time can be set by
using the LT command.
Associate
(D5 = 1
Device not joined)
A single commissioning button press when the device has not joined a network that
causes the associate pin to blink to indicate the AI Code where: AI = # blinks + 0x20.
In this example, AI = 0x22.
AD0/DIO0
The node identification frame is similar to the node discovery response frame – it contains the device’s address,
node identifier string (NI command), and other relevant data. All API devices that receive the node identification
frame send it out their UART as an API Node Identification Indicator frame (0x95).
Associate LED
The Associate pin (pin 15) can provide indication of the device’s network status and diagnostics information. To
take advantage of these indications, an LED can be connected to the Associate pin as shown in the figure above.
The Associate LED functionality is enabled by setting the D5 command to 1 (enabled by default). If enabled, the
Associate pin is configured as an output and will behave as described in the following sections.
Joined Indication
The Associate pin indicates the network status of a device. If the module is not joined to a network, the
Associate pin is set high. Once the module successfully joins a network, the Associate pin blinks at a regular
time interval. This is shown in the following figure.
JoinedStatusofaDevice
The LT command defines the blink time of the Associate pin. If set to 0, the device uses the default blink time
(500ms for coordinator, 250ms for routers and end devices).
Diagnostics Support
The Associate pin works with the commissioning pushbutton to provide additional diagnostics behaviors to aid in
deploying and testing a network. If the commissioning push button is pressed once, and the device has not
joined a network, the Associate pin blinks a numeric error code to indicate the cause of join failure. The number
of blinks is equal to (AI value – 0x20). For example, if AI=0x22, 2 blinks occur.
If the commissioning push button is pressed once, and the device has joined a network, the device transmits a
broadcast node identification packet. If the Associate LED functionality is enabled (D5 command), a device that
receives this transmission will blink its Associate pin rapidly for 1 second.
The following figures demonstrate these behaviors.
AI=0x22
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Associate Pin
(D5 = 1)
AD0/DIO0 Pi n
(Remote Device)
A single button press on a remote device causes a broadcast node identification transmission
to be sent. All devices that receive this transmission blink their associate pin rapidly for one
second if the associate LED functionality is enabled. (D5 = 1)
BroadcastNodeIdentificationTransmission
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7.ManagingEndDevices
ZigBee end devices are intended to be battery-powered devices capable of sleeping for extended periods of time. Since
end devices may not be awake to receive RF data at a given time, routers and coordinators are equipped with additional
capabilities (including packet buffering and extended transmission timeouts) to ensure reliable data delivery to end
devices.
End Device Operation
When an end device joins a ZigBee network, it must find a router or coordinator device that is allowing end devices
to join. Once the end device joins a network, a parent-child relationship is formed between the end device and the
router or coordinator that allowed it to join. See chapter 3 for details.
When the end device is awake, it sends poll request messages to its parent. When the parent receives a poll request,
it checks a packet queue to see if it has any buffered messages for the end device. It then sends a MAC layer
acknowledgment back to the end device that indicates if it has data to send to the end device or not.
If the end device receives the acknowledgment and finds that the parent has no data for it, the end device can
return to idle mode or sleep. Otherwise, it will remain awake to receive the data. This polling mechanism allows the
end device to enter idle mode and turn its receiver off when RF data is not expected in order to reduce current
consumption and conserve battery life.
The end device can only send data directly to its parent. If an end device must send a broadcast or a unicast
transmission to other devices in the network, it sends the message directly to its parent and the parent performs
any necessary route or address discoveries to route the packet to the final destination.
Parent Operation
Each router or coordinator maintains a child table that contains the addresses of its end device children. A router or
coordinator that has unused entries in its child table is said to have end device capacity, or the ability to allow new
end devices to join. If the child table is completely filled (such that the number of its end device children matches
the number of child table entries), the device cannot allow any more end devices to join to it.
Since the end device children are not guaranteed to be awake at a given time, the parent is responsible for
managing incoming data packets in behalf of its end device children. If a parent receives an RF data transmission
destined for one of its end device children, and if the parent has enough unused buffer space, it will buffer the
packet. The data packet will remain buffered until a timeout expires, or until the end device sends a poll request to
retrieve the data.
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The parent can buffer one broadcast transmission for all of its end device children. When a broadcast transmission is
received and buffered, the parent sets a flag in its child table when each child polls and retrieves the packet. Once all
children have received the broadcast packet, the buffered broadcast packet is discarded. If all children have not
received a buffered broadcast packet and a new broadcast is received, the old broadcast packet is discarded, the
child table flags are cleared, and the new broadcast packet is buffered for the end device children. This is
demonstrated in the figure below.
When an end device sends data to its parent that is destined for a remote device in the network, the parent buffers
the data packet until it can establish a route to the destination. The parent may perform a route or 16-bit address
discovery in behalf of its end device children. Once a route is established, the parent sends the data transmission to
the remote device.
End Device Poll Timeouts
To better support mobile end devices (end devices that can move around in a network), parent router and
coordinator devices have a poll timeout for each end device child. If an end device does not send a poll request
to its parent within the poll timeout, the parent will remove the end device from its child table. This allows the
child table on a router or coordinator to better accommodate mobile end devices in the network.
Packet Buffer Usage
Packet buffer usage on a router or coordinator varies depending on the application. The following activities can
require use of packet buffers for up to several seconds:
•Route and address discoveries
•Application broadcast transmissions
•Stack broadcasts (e.g. ZDO "Device Announce" messages when devices join a network)
•Unicast transmissions (buffered until acknowledgment is received from destination or retries exhausted)
•Unicast messages waiting for end device to wake.
Applications that use regular broadcasting or that require regular address or route discoveries will use up a
significant number of buffers, reducing the buffer availability for managing packets for end device children.
Applications should reduce the number of required application broadcasts, and consider implementing an
external address table or many-to-one and source routing if necessary to improve routing efficiency.
Non-Parent Device Operation
Devices in the ZigBee network treat data transmissions to end devices differently than transmissions to other
routers and coordinators. Recall that when a unicast transmission is sent, if a network acknowledgment is not
received within a timeout, the device resends the transmission. When transmitting data to remote coordinator or
router devices, the transmission timeout is relatively short since these devices are powered and responsive.
However, since end devices may sleep for some time, unicast transmissions to end devices use an extended timeout
mechanism in order to allow enough time for the end device to wake and receive the data transmission from its
parent.
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If a non-parent device does not know the destination is an end device, it will use the standard unicast timeout for
the transmission. However, provisions exist in the Ember ZigBee stack for the parent to inform the message sender
that the destination is an end device. Once the sender discovers the destination device is an end device, future
transmissions will use the extended timeout. See the XBee Router / Coordinator Configuration section in this chapter
for details.
XBee End Device Configuration
XBee end devices support two different sleep modes:
•Pin Sleep
•Cyclic Sleep.
Pin sleep allows an external microcontroller to determine when the XBee should sleep and when it should wake by
controlling the Sleep_RQ pin. In contrast, cyclic sleep allows the sleep period and wake times to be configured
through the use of AT commands. The sleep mode is configurable with the SM command.
In both pin and cyclic sleep modes, XBee end devices poll their parent every 100ms while they are awake to retrieve
buffered data. When a poll request has been sent, the end device enables the receiver until an acknowledgment is
received from the parent. (It generally takes less than 10ms from the time the poll request is sent until the
acknowledgment is received.) The acknowledgment indicates if the parent has buffered data for the end device child
or not. If the acknowledgment indicates the parent has pending data, the end device will leave the receiver on to
receive the data. Otherwise, the end device will turn off the receiver and enter idle mode (until the next poll request
is sent) to reduce current consumption (and improve battery life).
Once the module enters sleep mode, the On/Sleep pin (pin 13) is de-asserted (low) to indicate the module is
entering sleep mode. If CTS hardware flow control is enabled (D7 command), the CTS pin (pin 12) is de-asserted
(high) when entering sleep to indicate that serial data should not be sent to the module. The module will not
respond to serial or RF data when it is sleeping. Applications that must communicate serially to sleeping end devices
are encouraged to observe CTS flow control.
When the XBee wakes from sleep, the On/Sleep pin is asserted (high), and if flow control is enabled, the CTS pin is
also asserted (low). If the module has not joined a network, it will scan all SC channels after waking to try and find
a valid network to join.
Pin Sleep
Pin sleep allows the module to sleep and wake according to the state of the Sleep_RQ pin (pin 9). Pin sleep
mode is enabled by setting the SM command to 1.
When Sleep_RQ is asserted (high), the module will finish any transmit or receive operations and enter a low
power state. For example, if the module has not joined a network and Sleep_RQ is asserted (high), the module
will sleep once the current join attempt completes (i.e. when scanning for a valid network completes). The
module will wake from pin sleep when the Sleep_RQ pin is de-asserted (low).
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In the figure above, t1, t2, and t3 represent the following events:
•T1 - Time when Sleep_RQ is asserted (high)
•T2 - Time when the XBee enters sleep (CTS state change only if hardware flow control is enabled)
•T3 - Time when Sleep_RQ is de-asserted (low) and the module wakes.
The time between T1 and T2 varies depending on the state of the module. In the worst case scenario, if the end
device is trying to join a network, or if it is waiting for an acknowledgment from a data transmission, the delay
could be up to a few seconds.
When the XBee is awake and is joined to a network, it sends a poll request to its parent to see if the parent has
any buffered data for it. The end device will continue to send poll requests every 100ms while it is awake.
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DemonstrationofPinSleep
Parent and remote devices must be configured to buffer data correctly and to utilize adequate transmission
timeouts. See the XBee Router / Coordinator Configuration section in this chapter for details.
Cyclic Sleep
Cyclic sleep allows the module to sleep for a specified time and wake for a short time to poll its parent for any
buffered data messages before returning to sleep again. Cyclic sleep mode is enabled by setting the SM
command to 4 or 5. SM5 is a slight variation of SM4 that allows the module to be woken prematurely by
asserting the Sleep_RQ pin (pin 9). In SM5, the XBee can wake after the sleep period expires, or if a high-tolow transition occurs on the Sleep_RQ pin. Setting SM to 4 disables the pin wake option.
In cyclic sleep, the module sleeps for a specified time, and then wakes and sends a poll request to its parent to
discover if the parent has any pending data for the end device. If the parent has buffered data for the end
device, or if serial data is received, the XBee will remain awake for a time. Otherwise, it will enter sleep mode
immediately.
The On/Sleep line is asserted (high) when the module wakes, and is de-asserted (low) when the module sleeps.
If hardware flow control is enabled (D7 command), the CTS pin will assert (low) when the module wakes and
can receive serial data, and de-assert (high) when the module sleeps.
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In the figure above, t1, t2, and t3 represent the following events:
•T1 - Time when the module wakes from cyclic sleep
•T2 - Time when the module returns to sleep
•T3 - Later time when the module wakes from cyclic sleep.
The wake time and sleep time are configurable with software commands as described in the sections below.
Wake Time (Until Sleep)
In cyclic sleep mode (SM=4 or 5), if serial or RF data is received, the module will start a sleep timer (time
until sleep). Any data received serially or over the RF link will restart the timer. The sleep timer value is
settable with the ST command. While the module is awake, it will send poll request transmissions every
100ms to check its parent for buffered data messages. The module returns to sleep when the sleep timer
expires, or if the SI command is sent to it. The following image shows this behavior.
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DIN
A cyclic sleep end device enters sleep mode when no serial or RF data is received for ST time .
ST = Time Awake
On/Sleep
Legend
On/Sleep
Transmitting Poll
Request
Sleep Period
The sleep period is configured based on the SP, SN, and SO commands. The following table lists the
behavior of these commands.
Command Range Description
SP
SN
0x20 - 0xAF0 (x 10 ms)
(320 - 28,000 ms)
1 - 0xFFFF
Configures the sleep period of the module.
Configures the number of sleep periods
multiplier.
Defines options for sleep mode behavior.
SO
0 - 0xFF
0x02 - Always wake for full ST time
0x04 - Enable extended sleep (sleep for full
(SP * SN) time)
The XBee module supports both a short cyclic sleep and an extended cyclic sleep that make use of these
commands. These two modes allow the sleep period to be configured according to the application
requirements.
Short Cyclic Sleep
In short cyclic sleep mode, the sleep behavior of the module is defined by the SP and SN commands, and
the SO command must be set to 0x00 (default) or 0x02. In short cyclic sleep mode, the SP command
defines the sleep period and is settable up to 28 seconds. When the XBee enters short cyclic sleep, it
remains in a low power state until the SP time has expired.
After the sleep period expires, the XBee sends a poll request transmission to its parent to determine if its
parent has any buffered data waiting for the end device. Since router and coordinator devices can buffer
data for end device children up to 30 seconds, the SP range (up to 28 seconds) allows the end device to poll
regularly enough to receive buffered data. If the parent has data for the end device, the end device will
start its sleep timer (ST) and continue polling every 100ms to receive data. If the end device wakes and
finds that its parent has no data for it, the end device can return to sleep immediately.
The SN command can be used to control when the On/Sleep line is asserted (high). If SN is set to 1
(default), the On/Sleep line will be set high each time the XBee wakes from sleep. Otherwise, if SN is
greater than 1, the On/Sleep line will only be set high if RF data is received, or after SN wake cycles occur.
This allows an external device to remain powered off until RF data is received, or until a number of sleep
periods have expired (SN sleep periods). This mechanism allows the XBee to wake at regular intervals to
poll its parent for data without waking an external device for an extended time (SP * SN time). This is
shown in the figure below.
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On/Sleep
Δt = SP
Δt = SP * SN
(SN = 1)
Setting SN > 1 allows the XBee to silently poll for data without asserting On /Sleep. If RF data is received
when polling, On/Sleep will immediately assert .
Transmitting poll request to parent
Δt = SP
Sleep_RQ
Transmitting Poll
Reques t
Legend
Δt = SP * SN
On/Sleep
(SN = 3)
Transmitting poll request to parent
Transmitting RF Data
Receiving RF Data
Note: SP controls the packet buffer time on routers and coordinators. SP should be set on all router and
coordinator devices to match the longest end device SP time. See the XBee Router / Coordinator
Configuration section for details.
Extended Cyclic Sleep
In extended cyclic sleep operation, an end device can sleep for a multiple of SP time which can extend the
sleep time up to several days. The sleep period is configured using the SP and SN commands. The total
sleep period is equal to (SP * SN) where SP is measured in 10ms units. The SO command must be set
correctly to enable extended sleep.
Since routers and coordinators can only buffer incoming RF data for their end device children for up to 30
seconds, if an end device sleeps longer than 30 seconds, devices in the network need some indication when
an end device is awake before they can send data to it. End devices that use extended cyclic sleep should
send a transmission (such as an IO sample) when they wake to inform other devices that they are awake
and can receive data. It is recommended that extended sleep end devices set SO to wake for the full ST
time in order to provide other devices with enough time to send messages to the end device.
Similar to short cyclic sleep, end devices running in this mode will return to sleep when the sleep timer
expires, or when the SI command is received.
An end device may transmit data when it wakes from sleep and has joined a network. End devices transmit
directly to their parent and then wait for an acknowledgment to be received. The parent will perform any
required address and route discoveries to help ensure the packet reaches the intended destination before
reporting the transmission status to the end device.
After waking from sleep, an end device sends a poll request to its parent to determine if the parent has any
buffered data for it. In pin sleep mode, the end device polls every 100ms while the Sleep_RQ pin is de-asserted
(low). In cyclic sleep mode, the end device will only poll once before returning to sleep unless the sleep timer
(ST) is started (serial or RF data is received). If the sleep timer is started, the end device will continue to poll
every 100ms until the sleep timer expires.
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The XBee ZB 2x6x firmware includes an adaptive polling enhancement where, if an end device receives RF data
from its parent, it sends another poll after a very short delay to check for more data. The end device continues
to poll at a faster rate as long as it receives data from its parent. This feature greatly improves data throughput
to end devices. When the end device no longer receives data from its parent, it resumes polling every 100ms.
IO Sampling
End devices can be configured to send one or more IO samples when they wake from sleep. To enable IO
sampling on an end device, the IR command must be set to a non-zero value, and at least one analog or digital
IO pin must be enabled for sampling (D0 - D9, P0-P2 commands). If IO sampling is enabled, an end device
sends an IO sample when it wakes and starts the ST timer. It will continue sampling at the IR rate until the
sleep timer (ST) has expired. See chapter 8 for details.
Waking End Devices with the Commissioning Pushbutton
If the commissioning pushbutton functionality is enabled (D0 command), a high-to-low transition on the AD0/
DIO0 pin (pin 20) will cause an end device to wake for 30 seconds. See the Commissioning Pushbutton section
in chapter 7 for details.
Parent Verification
Since an end device relies on its parent to maintain connectivity with other devices in the network, XBee end
devices include provisions to verify its connection with its parent. End devices monitor their link with their
parent when sending poll messages and after a power cycle or reset event as described below.
When an end device wakes from sleep, it sends a poll request to its parent. In cyclic sleep, if RF or serial data is
not received and the sleep timer is not started, the end device polls one time and returns to sleep for another
sleep period. Otherwise, the end device continues polling every 100ms. If the parent does not send an
acknowledgment response to three consecutive poll request transmissions, the end device assumes the parent
is out of range, and attempts to find a new parent.
After a power-up or reset event, the end device does an orphan scan to locate its parent. If the parent does not
send a response to the orphan scan, the end device attempts to find a new parent.
Rejoining
Once all devices have joined a ZigBee network, the permit-joining attribute should be disabled such that new
devices are no longer allowed to join the network. Permit-joining can be enabled later as needed for short
times. This provides some protection in preventing other devices from joining a live network.
If an end device cannot communicate with its parent, the end device must be able to join a new parent to
maintain network connectivity. However, if permit-joining is disabled in the network, the end device will not find
a device that is allowing new joins.
To overcome this problem, ZigBee supports rejoining, where an end device can obtain a new parent in the same
network even if joining is not enabled. When an end device joins using rejoining, it performs a PAN ID scan to
discover nearby networks. If a network is discovered that has the same 64-bit PAN ID as the end device, it will
join the network by sending a rejoin request to one of the discovered devices. The device that receives the
rejoin request will send a rejoin response if it can allow the device to join the network (i.e. child table not full).
The rejoin mechanism can be used to allow a device to join the same network even if permit-joining is disabled.
To enable rejoining, NJ should be set less than 0xFF on the device that will join. If NJ < 0xFF, the device
assumes the network is not allowing joining and first tries to join a network using rejoining. If multiple rejoining
attempts fail, or if NJ=0xFF, the device will attempt to join using association.
XBee Router/Coordinator Configuration
XBee routers and coordinators may require some configuration to ensure the following are set correctly:
•RF packet buffering timeout
•Child poll timeout
•Transmission timeout.
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The value of these timeouts depends on the sleep time used by the end devices. Each of these timeouts are
discussed below.
RF Packet Buffering Timeout
When a router or coordinator receives an RF data packet intended for one of its end device children, it buffers
the packet until the end device wakes and polls for the data, or until a packet buffering timeout occurs. This
timeout is settable using the SP command. The actual timeout is (1.2 * SP), with a minimum timeout of 1.2
seconds and a maximum of 30 seconds. Since the packet buffering timeout is set slightly larger than the SP
setting, SP should be set the same on routers and coordinators as it is on cyclic sleep end devices. For pin sleep
devices, SP should be set as long as the pin sleep device can sleep, up to 30 seconds.
Note: In pin sleep and extended cyclic sleep, end devices can sleep longer than 30 seconds. If end devices sleep
longer than 30 seconds, parent and non-parent devices must know when the end device is awake in order to
reliably send data. For applications that require sleeping longer than 30 seconds, end devices should transmit
an IO sample or other data when they wake to alert other devices that they can send data to the end device.
Child Poll Timeout
Router and coordinator devices maintain a timestamp for each end device child indicating when the end device
sent its last poll request to check for buffered data packets. If an end device does not send a poll request to its
parent for a certain period of time, the parent will assume the end device has moved out of range and will
remove the end device from its child table. This allows routers and coordinators to be responsive to changing
network conditions. The NC command can be issued at any time to read the number of remaining (unused) child
table entries on a router or coordinator.
The child poll timeout is settable with the SP and SN commands. SP and SN should be set such that SP * SN
matches the longest expected sleep time of any end devices in the network. The actual timeout is calculated as
(3 * SP * SN), with a minimum of 5 seconds. For networks consisting of pin sleep end devices, the SP and SN
values on the coordinator and routers should be set such that SP * SN matches the longest expected sleep
period of any pin sleep device. The 3 multiplier ensures the end device will not be removed unless 3 sleep cycles
pass without receiving a poll request. The poll timeout is settable up to a couple of months.
Adaptive Polling
The PO command determines the regular polling rate. However, if RF data has been recently received by an end
device, it is likely that yet more RF data could be on the way. Therefore, the end device will poll at a faster rate,
gradually decreasing its adaptive poll rate until polling resumes at the regular rate as defined by the PO
command.
Transmission Timeout
As mentioned in chapter 4, when sending RF data to a remote router, since routers are always on, the timeout
is based on the number of hops the transmission may traverse. This timeout it settable using the NH command.
(See chapter 4 for details.)
Since end devices may sleep for lengthy periods of time, the transmission timeout to end devices also includes
some allowance for the sleep period of the end device. When sending data to a remote end device, the
transmission timeout is calculated using the SP and NH commands. If the timeout occurs and an
acknowledgment has not been received, the source device will resend the transmission until an
acknowledgment is received, up to two more times.
The transmission timeout per attempt is:
3 * ((unicast router timeout) + (end device sleep time)), or
3 * ((50 * NH) + (1.2 * SP)), where SP is measured in 10ms units.
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Putting it all Together
Short Sleep Periods
Pin and cyclic sleep devices that sleep less than 30 seconds can receive data transmissions at any time since
their parent device(s) will be able to buffer data long enough for the end devices to wake and poll to receive the
data. SP should be set the same on all devices in the network. If end devices in a network have more than one
SP setting, SP on the routers and coordinators should be set to match the largest SP setting of any end device.
This will ensure the RF packet buffering, poll timeout, and transmission timeouts are set correctly.
Extended Sleep Periods
Pin and cyclic sleep devices that might sleep longer than 30 seconds cannot receive data transmissions reliably
unless certain design approaches are taken. Specifically, the end devices should use IO sampling or another
mechanism to transmit data when they wake to inform the network they can receive data. SP and SN should be
set on routers and coordinators such that (SP * SN) matches the longest expected sleep time. This configures
the poll timeout so end devices are not expired from the child table unless a poll request is not received for 3
consecutive sleep periods.
As a general rule of thumb, SP and SN should be set the same on all devices in almost all cases.
Sleep Examples
This section covers some sample XBee configurations to support different sleep modes. Several AT commands are
listed with suggested parameter values. The notation in this section includes an '=' sign to indicate what each
command register should be set to - for example, SM=4. This is not the correct notation for setting command values
in the XBee. In AT command mode, each command is issued with a leading 'AT' and no '=' sign - for example ATSM4.
In the API, the two byte command is used in the command field, and parameters are populated as binary values in
the parameter field.
Example 1
Configure a device to sleep for 20 seconds, but set SN such that the On/Sleep line will remain deasserted for up to 1 minute.
The following settings should be configured on the end device.
SM = 4 (cyclic sleep) or 5 (cyclic sleep, pin wake)
SP = 0x7D0 (2000 decimal). This causes the end device to sleep for 20 seconds since SP is measured in units of
10ms.
SN = 3. (With this setting, the On/Sleep pin will assert once every 3 sleep cycles, or when RF data is received)
SO = 0
All router and coordinator devices on the network should set SP to match SP on the end device. This ensures
that RF packet buffering times and transmission timeouts will be set correctly.
Since the end device wakes after each sleep period (ATSP), the SN command can be set to 1 on all routers and
the coordinator.
Example 2
Configure an end device to sleep for 20 seconds, send 4 IO samples in 2 seconds, and return to
sleep.
Since SP is measured in 10ms units, and ST and IR are measured in 1ms units, configure an end device with the
following settings:
SM = 4 (cyclic sleep) or 5 (cyclic sleep, pin wake)
SP = 0x7D0 (2000 decimal). This causes the end device to sleep for 20 seconds.
SN = 1
SO = 0
ST = 0x7D0 (2000 decimal). This sets the sleep timer to 2 seconds.
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IR = 0x258 (600 decimal). Set IR to a value greater than (2 seconds / 4) to get 4 samples in 2 seconds. The
end device sends an IO sample at the IR rate until the sleep timer has expired.
At least one analog or digital IO line must be enabled for IO sampling to work. To enable pin 19 (AD1/DIO1) as
a digital input line, the following must be set:
D1 = 3
All router and coordinator devices on the network should set SP to match SP on the end device. This ensures
that RF packet buffering times and transmission timeouts will be set correctly.
Example 3
Configure a device for extended sleep: to sleep for 4 minutes.
SP and SN must be set such that SP * SN = 4 minutes. Since SP is measured in 10ms units, the following
settings can be used to obtain 4 minute sleep.
SM = 4 (cyclic sleep) or 5 (cyclic sleep, pin wake)
SP = 0x7D0 (2000 decimal, or 20 seconds)
SN = 0x0B (12 decimal)
SO = 0x04 (enable extended sleep)
With these settings, the module will sleep for SP * SN time, or (20 seconds * 12) = 240 seconds = 4 minutes.
For best results, the end device should send a transmission when it wakes to inform the coordinator (or
network) when it wakes. It should also remain awake for a short time to allow devices to send data to it. The
following are recommended settings.
ST = 0x7D0 (2 second wake time)
SO = 0x06 (enable extended sleep and wake for ST time)
IR = 0x800 (send 1 IO sample after waking). At least one analog or digital IO sample should be enabled for IO
sampling.
With these settings, the end device will wake after 4 minutes and send 1 IO sample. It will then remain awake
for 2 seconds before returning to sleep.
SP and SN should be set to the same values on all routers and coordinators that could allow the end device to
join. This will ensure the parent does not timeout the end device from its child table too quickly.
The SI command can optionally be sent to the end device to cause it to sleep before the sleep timer expires.
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8.XBeeAnalogandDigitalIOLines
XBee ZB firmware supports a number of analog and digital IO pins that are configured through software commands.
Analog and digital IO lines can be set or queried. The following table lists the configurable IO pins and the corresponding
configuration commands.
Module Pin Names Module Pin Numbers Configuration Command
CD/DIO12 4 P2
PWM0/RSSIM/DIO10 6 P0
PWM/DIO11 7 P1
DIO4 11 D4
CTS/DIO7 12 D7
ASSOC/DIO5 15 D5
RTS/DIO6 16 D6
AD3/DIO3 17 D3
AD2/DIO2 18 D2
AD1/DIO1 19 DI
AD0/DIO0 20 D0
IO Configuration
To enable an analog or digital IO function on one or more XBee module pin(s), the appropriate configuration
command must be issued with the correct parameter. After issuing the configuration command, changes must be
applied on the module for the IO settings to take effect.
Pin Command Parameter Description
0 Unmonitored digital input
1 Reserved for pin-specific alternate functionalities
2 Analog input, single ended (A/D pins only)
3 Digital input, monitored
4 Digital output, default low
5 Digital output, default high
6-9 Alternate functionalities, where applicable
Pull-up resistors can be set for each digital input line using the PR command. The PR value updates the state of all
pull-up resistors.
IO Sampling
The XBee ZB modules have the ability to monitor and sample the analog and digital IO lines. IO samples can be read
locally or transmitted to a remote device to provide indication of the current IO line states. (Only API firmware
devices can send remote IO sample data out their UART.)
There are three ways to obtain IO samples, either locally or remotely:
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•Queried Sampling
•Periodic Sampling
•Change Detection Sampling.
IO sample data is formatted as shown in the table below
Bytes Name Description
1 Sample Sets Number of sample sets in the packet. (Always set to 1.)
2 Digital Channel Mask
1 Analog Channel Mask
Variable Sampled Data Set
Indicates which digital IO lines have sampling enabled. Each bit corresponds to one
digital IO line on the module.
• bit 0 = AD0/DIO0
• bit 1 = AD1/DIO1
• bit 2 = AD2/DIO2
• bit 3 = AD3/DIO3
• bit 4 = DIO4
• bit 5 = ASSOC/DIO5
•bit 6 = RTS/DIO6
•bit 7 = CTS/GPIO7
• bit 8 = N/A
• bit 9 = N/A
• bit 10 = RSSI/DIO10
• bit 11 = PWM/DIO11
• bit 12 = CD/DIO12
For example, a digital channel mask of 0x002F means DIO0,1,2,3, and 5 are enabled
as digital IO.
Indicates which lines have analog inputs enabled for sampling. Each bit in the analog
channel mask corresponds to one analog input channel.
• bit 0 = AD0/DIO0
• bit 1 = AD1/DIO1
• bit 2 = AD2/DIO2
• bit 3 = AD3/DIO3
• bit 7 = Supply Voltage
A sample set consisting of 1 sample for each enabled ADC and/or DIO channel,
which has voltage inputs of 1143.75 and 342.1875mV.
If any digital IO lines are enabled, the first two bytes of the data set indicate the state
of all enabled digital IO. Only digital channels that are enabled in the Digital Channel
Mask bytes have any meaning in the sample set. If no digital IO are enabled on the
device, these 2 bytes will be omitted.
Following the digital IO data (if any), each enabled analog channel will return 2 bytes.
The data starts with AIN0 and continues sequentially for each enabled analog input
channel up to AIN3, and the supply voltage (if enabled) at the end.
The sampled data set will include 2 bytes of digital IO data only if one or more IO lines on the device are configured
as digital IO. If no pins are configured as digital IO, these 2 bytes will be omitted.
The digital IO data is only relevant if the same bit is enabled in the digital IO mask.
Analog samples are returned as 10-bit values. The analog reading is scaled such that 0x0000 represents 0V, and
0x3FF = 1.2V. (The analog inputs on the module cannot read more than 1.2V.) Analog samples are returned in order
starting with AIN0 and finishing with AIN3, and the supply voltage. Only enabled analog input channels return data
as shown in the figure below.
To convert the A/D reading to mV, do the following:
AD(mV) = (A/D reading * 1200mV) / 1023
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XBee®/XBee‐PRO®ZBRFModules
The reading in the sample frame represents voltage inputs of 1143.75 and 342.1875mV for AD0 and AD1
respectively.
Queried Sampling
The IS command can be sent to a device locally, or to a remote device using the API remote command frame
(see chapter 8 for details). When the IS command is sent, the receiving device samples all enabled digital IO
and analog input channels and returns an IO sample. If IS is sent locally, the IO sample is sent out the UART. If
the IS command was received as a remote command, the IO sample is sent over-the-air to the device that sent
the IS command.
If the IS command is issued in AT firmware, the module returns a carriage return-delimited list containing the
above-listed fields. The API firmware returns an AT command response packet with the IO data included in the
command data portion of the response frame.
The following table shows an example of the fields in an IS response.
0x01 [1 sample set]
0x0C0C [Digital Inputs: DIO 2, 3, 10, 11 low]
0x03 [Analog Inputs: A/D 0, 1]
0x0408 [Digital input states: DIO 3, 10 high, DIO 2, 11 low]
0x03D0 [Analog input ADIO 0= 0x3D0]
0x0124 [Analog input ADIO 1=0x120]
Example Sample AT Response
Periodic IO Sampling
Periodic sampling allows an XBee/XBee-PRO module to take an IO sample and transmit it to a remote device at
a periodic rate. The periodic sample rate is set by the IR command. If IR is set to 0, periodic sampling is
disabled. For all other values of IR, data will be sampled after IR milliseconds have elapsed and transmitted to a
remote device. The DH and DL commands determine the destination address of the IO samples. DH and DL can
be set to 0 to transmit to the coordinator, or to the 64-bit address of the remote device (SH and SL). Only
devices running API firmware can send IO data samples out their UART. Devices running AT firmware will
discard received IO data samples.
A sleeping end device will transmit periodic IO samples at the IR rate until the ST timer expires and the device
can resume sleeping.
Change Detection Sampling
Modules can be configured to transmit a data sample immediately whenever a monitored digital IO pin changes
state. The IC command is a bitmask that can be used to set which digital IO lines should be monitored for a
state change. If one or more bits in IC is set, an IO sample will be transmitted as soon as a state change is
observed in one of the monitored digital IO lines. Change detection samples are transmitted to the 64-bit
address specified by DH and DL.
RSSI PWM
The XBee module features an RSSI/PWM pin (pin 6) that, if enabled, will adjust the PWM output to indicate the
signal strength of the last received packet. The P0 (P-zero) command is used to enable the RSSI pulse width
modulation (PWM) output on the pin. If P0 is set to 1, the RSSI/PWM pin will output a pulse width modulated signal
where the frequency is adjusted based on the received signal strength of the last packet. Otherwise, for all other P0
settings, the pin can be used for general purpose IO.
When a data packet is received, if P0 is set to enable the RSSI/PWM feature, the RSSI PWM output is adjusted based
on the RSSI of the last packet. The RSSI/PWM output will be enabled for a time based on the RP command. Each
time an RF packet is received, the RSSI/PWM output is adjusted based on the RSSI of the new packet, and the RSSI
timer is reset. If the RSSI timer expires, the RSSI/PWM pin is driven low. RP is measured in 100ms units and
defaults to a value of 40 (4 seconds).
The RSSI PWM runs at 12MHz and has 2400 total counts (200us period).
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XBee®/XBee‐PRO®ZBRFModules
RSSI (in dBm) is converted to PWM counts using the following equation:
PWM counts = (41 * RSSI_Unsigned) - 5928
IO Examples
Example 1: Configure the following IO settings on the XBee.
Configure AD1/DIO1 as a digital input with pullup resistor enabled
Configure AD2/DIO2 as an analog input
Configure DIO4 as a digital output, driving high.
To configure AD1/DIO1 as an input, issue the ATD1 command with a parameter of 3 ("ATD13"). To enable pullup resistors on the same pin, the PR command should be issued with bit 3 set (e.g. ATPR8, ATPR1FFF, etc.).
The ATD2 command should be issued with a parameter of 2 to enable the analog input ("ATD22"). Finally, DIO4
can be set as an output, driving high by issuing the ATD4 command with a parameter value of 5 ("ATD45").
After issuing these commands, changes must be applied before the module IO pins will be updated to the new
states. The AC or CN commands can be issued to apply changes (e.g. ATAC).
Example 2: Calculate the PWM counts for a packet received with an RSSI of -84dBm.
RSSI = -84 = 0xAC = 172 decimal (unsigned)
PWM counts = (41 * 172) - 5928
PWM counts = 1124
With a total of 2400 counts, this yields an ON time of (1124 / 2400) = 46.8%
Example 3: Configure the RSSI/PWM pin to operate for 2 seconds after each received RF packet.
First, ensure the RSSI/PWM functionality is enabled by reading the P0 (P-zero) command. It should be set to 1
(default).
To configure the duration of the RSSI/PWM output, set the RP command. To achieve a 2 second PWM output, set
RP to 0x14 (20 decimal, or 2 seconds) and apply changes (AC command).
After applying changes, all received RF data packets should set the RSSI timer for 2 seconds.
©2011DigiInternational,Inc. 98
9.APIOperation
Length
(Bytes 2-3)
Checksum
(Byte n + 1)
MSB LSB 1 Byte
Start Delimiter
(Byte 1)
0x7E
Frame Data
(Bytes 4-n)
API-specific Structure
Start Delimiter
(Byte 1)
Length
(Bytes 2-3)
Frame Data
(Bytes 4-n)
Checksum
(Byte n + 1)
0x7E MSB LSB API-specific Structure 1 Byte
Characters Escaped If Needed
As an alternative to Transparent Operation, API (Application Programming Interface) Operations are available. API
operation requires that communication with the module be done through a structured interface (data is communicated in
frames in a defined order). The API specifies how commands, command responses and module status messages are sent
and received from the module using a UART Data Frame.
Please note that Digi may add new API frames to future versions of firmware, so please build into your software interface
the ability to filter out additional API frames with unknown Frame Types.
API Frame Specifications
Two API modes are supported and both can be enabled using the AP (API Enable) command. Use the following AP
parameter values to configure the module to operate in a particular mode:
•AP = 1: API Operation
•AP = 2: API Operation (with escaped characters)
API Operation (AP parameter = 1)
When this API mode is enabled (AP = 1), the UART data frame structure is defined as follows:
UARTDataFrameStructure:
MSB=MostSignificantByte,LSB=LeastSignificantByte
Any data received prior to the start delimiter is silently discarded. If the frame is not received correctly or if
the checksum fails, the module will reply with a module status frame indicating the nature of the failure.
API Operation - with Escape Characters (AP parameter = 2)
When this API mode is enabled (AP = 2), the UART data frame structure is defined as follows:
UARTDataFrameStructure‐withescapecontrolcharacters:
MSB=MostSignificantByte,LSB=LeastSignificantByte
Escape characters. When sending or receiving a UART data frame, specific data values must be escaped
(flagged) so they do not interfere with the data frame sequencing. To escape an interfering data byte,
insert 0x7D and follow it with the byte to be escaped XOR’d with 0x20.
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XBee®/XBee‐PRO®ZBRFModules
Length
(Bytes 2-3)
Checksum
(Byte n + 1)
MSB LSB 1 Byte
Start Delimiter
(Byte 1)
0x7E
Frame Data
(Bytes 4-n)
API-specific Structure
Identifier-specific Data
cmdData
API Identifier
cmdID
Data bytes that need to be escaped:
•0x7E – Frame Delimiter
•0x7D – Escape
•0x11 – XON
•0x13 – XOFF
Example - Raw UART Data Frame (before escaping interfering bytes):
0x7E 0x00 0x02 0x23 0x11 0xCB
0x11 needs to be escaped which results in the following frame:
0x7E 0x00 0x02 0x23 0x7D 0x31 0xCB
Note: In the above example, the length of the raw data (excluding the checksum) is 0x0002 and the
checksum of the non-escaped data (excluding frame delimiter and length) is calculated as:
0xFF - (0x23 + 0x11) = (0xFF - 0x34) = 0xCB.
Length
The length field has a two-byte value that specifies the number of bytes that will be contained in the frame
data field. It does not include the checksum field.
Frame Data
Frame data of the UART data frame forms an API-specific structure as follows:
UARTDataFrame&API‐specificStructure:
The cmdID frame (API-identifier) indicates which API messages will be contained in the cmdData frame
(Identifier-specific data). Note that multi-byte values are sent big endian.The XBee modules support the
following API frames:
APIFrameNamesandVal u e s
API Frame Names API ID
AT Command - Queue Parameter Value
ZigBee Transmit Request 0x10
Explicit Addressing ZigBee Command Frame 0x11
Remote Command Request
AT Command Response
ZigBee Receive Packet (AO=0) 0x90
ZigBee Explicit Rx Indicator (AO=1) 0x91
ZigBee IO Data Sample Rx Indicator 0x92
XBee Sensor Read Indicator (AO=0) 0x94
Node Identification Indicator (AO=0) 0x95
Remote Command Response
Over-the-Air Firmware Update Status
Many-to-One Route Request Indicator
AT Command
0x08
0x09
0x17
Create Source Route
0x21
0x88
Modem Status 0x8A
ZigBee Transmit Status 0x8B
0x97
0xA0
Route Record Indicator
0xA1
0xA3
©2011DigiInternational,Inc. 100
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