Digi XBS6 User Manual

XBee® Wi-Fi RF Modules

XBee® Wi-Fi RF Module

This manual describes the operation of the XBee® Wi-Fi RF module, which consists of 802.11 bgn firmware loaded onto XBee® hardware. The XBee® Wi-Fi RF Modules are designed to operate within the 802.11 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 and wireless 802.11 b, g or n access points and routers. The modules operate within the ISM 2.4 GHz frequency band.

Digi International Inc. 11001 Bren Road East Minnetonka, MN 55343 877 912-3444 or 952 912-3444

http://www.digi.com

No part of the contents of this manual may be transmitted or reproduced in any form or by any means without the written permission of Digi International, Inc. XBee® is a registered trademark of Digi International, 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] Online Support: http://www.digi.com/support/eservice/login.jsp Email: rf-experts@digi.com

XBee® Wi-Fi RF Modules

Contents

1. Overview ............................................................................................................................................. 5

Specifications ...................................................................................................................................... 6

General Specifications .................................................................................................................... 6

RF Specifications ............................................................................................................................. 7

Electrical Specifications ................................................................................................................ 11

Environmental Specifications ....................................................................................................... 11

Serial Communications Specifications .......................................................................................... 12

UART ............................................................................................................................................. 12

SPI ................................................................................................................................................. 12

GPIO Specifications ........................................................................................................................... 13

Agency Approvals ............................................................................................................................. 14

Pin Signals ......................................................................................................................................... 14

Design Notes ..................................................................................................................................... 15

Power Supply ................................................................................................................................ 15

Recommended Pin Connections .................................................................................................. 15

Board Layout ................................................................................................................................ 16

Mounting Considerations ............................................................................................................. 18

2. RF Module Operation ....................................................................................................................... 19

Serial Communications ..................................................................................................................... 19

UART Communications ................................................................................................................. 19

SPI Communications ..................................................................................................................... 20

Serial Buffers .................................................................................................................................... 21

Serial Receive Buffer ..................................................................................................................... 21

Serial Transmit Buffer ................................................................................................................... 21

UART Flow Control ....................................................................................................................... 21

Serial Interface Protocols ................................................................................................................. 22

Transparent Operation ................................................................................................................. 22

API Operation ............................................................................................................................... 23

A Comparison of Transparent and API Operation ........................................................................ 23

Modes of Operation ......................................................................................................................... 24

Idle Mode ..................................................................................................................................... 24

Transmit Mode ............................................................................................................................. 24

Receive Mode ............................................................................................................................... 24

Command Mode ........................................................................................................................... 24

XBee® Wi-Fi RF Modules

Sleep Mode ....................................................................................................................................... 26

3. 802.11 bgn Networks ....................................................................................................................... 27

Infrastructure Networks ................................................................................................................... 27

Ad Hoc Networks .............................................................................................................................. 27

Network Basics ................................................................................................................................. 28

XBee® Wi-Fi Standards ..................................................................................................................... 28

Encryption ........................................................................................................................................ 28

CHANNELS ........................................................................................................................................ 29

4. XBee IP Services ................................................................................................................................ 29

XBee Application Service .................................................................................................................. 30

Local Host ..................................................................................................................................... 30

Network Client .............................................................................................................................. 31

Serial Communication Service .......................................................................................................... 34

Transparent mode ........................................................................................................................ 34

API mode ...................................................................................................................................... 34

5. Sleep ................................................................................................................................................. 35

Sleeping with the UART .................................................................................................................... 35

Sleeping with the SPI ........................................................................................................................ 35

Sleep Options ................................................................................................................................... 36

AP Associated sleep ...................................................................................................................... 36

Deep sleep (non-associated sleep) ............................................................................................... 36

Sampling data using sleep modes .................................................................................................... 37

Sample Rate (ATIR) ....................................................................................................................... 37

Wake Host .................................................................................................................................... 37

6. XBee Analog and Digital IO Lines ...................................................................................................... 38

IO Sampling ....................................................................................................................................... 38

Queried Sampling ......................................................................................................................... 40

Periodic IO Sampling ..................................................................................................................... 40

I/O Examples ................................................................................................................................. 41

7. API Operation ................................................................................................................................... 42

API Frame Specifications .................................................................................................................. 42

API UART and SPI Exchanges ............................................................................................................ 45

AT Commands ............................................................................................................................... 45

Transmitting and Receiving RF Data ............................................................................................. 45

Remote AT commands ................................................................................................................. 46

XBee® Wi-Fi RF Modules

Supporting the API ........................................................................................................................ 46

API Frames ........................................................................................................................................ 47

TX (Transmit) request: 64-Bit ....................................................................................................... 47

AT Command ................................................................................................................................ 47

AT Command-Queue Parameter Value ........................................................................................ 48

Remote AT Command Request .................................................................................................... 49

Transmit (TX) request: IPv4 .......................................................................................................... 51

AT Command Response ................................................................................................................ 52

Modem Status .............................................................................................................................. 53

Transmission Status ...................................................................................................................... 54

IO Data Sample RX Indicator ........................................................................................................ 55

Remote Command Response ....................................................................................................... 57

RX (Receive) Packet: IPv4 ............................................................................................................. 58

8. XBee Command Reference Tables.................................................................................................... 59

Addressing ........................................................................................................................................ 59

Networking Commands .................................................................................................................... 60

Security Commands .......................................................................................................................... 60

RF Interfacing Commands ................................................................................................................ 60

Serial Interfacing ............................................................................................................................... 61

I/O Settings ....................................................................................................................................... 62

Diagnostics Interfacing ..................................................................................................................... 65

AT Command Options ...................................................................................................................... 66

Sleep Commands .............................................................................................................................. 66

Execution Commands ....................................................................................................................... 67

9. Module Support ................................................................................................................................ 68

X-CTU Configuration Tool ................................................................................................................ 68

Serial Firmware Updates ............................................................................................................. 68

Regulatory Compliance ................................................................................................................ 68

Agency Certifications ................................................................................................................... 68

United States FCC ............................................................................................................................. 68

OEM Labeling Requirements ....................................................................................................... 69

FCC Notices ................................................................................................................................... 69

FCC-Approved Antennas (2.4 GHz) .............................................................................................. 70

RF Exposure .................................................................................................................................. 73

Europe (ETSI) .................................................................................................................................... 74

XBee® Wi-Fi RF Modules

OEM Labeling Requirements ....................................................................................................... 74

Restrictions .................................................................................................................................. 74

Declarations of Conformity ......................................................................................................... 74

Approved Antennas ..................................................................................................................... 75

XBee RF Module ........................................................................................................................... 75

Canada (IC) ....................................................................................................................................... 76

Transmitters with Detachable Antennas .................................................................................... 76

Detachable Antenna .................................................................................................................... 76

Australia (C-Tick) .............................................................................................................................. 77

10. Warranty Information .................................................................................................................... 78

1-Year Warranty............................................................................................................................... 78

Appendix A: Definitions ...................................................................................................................... 79

1. Overview

The XBee® Wi-Fi RF module provides wireless connectivity to end-point devices in 802.11 bgn networks. Utilizing the 802.11 feature set, these modules are interoperable with other 802.11 bgn devices, including devices from other vendors. With XBee, users can have their 802.11 bgn network up-and running in a matter of minutes.

The XBee® Wi-Fi modules are compatible with other devices that use 802.11 bgn technology.

These include Digi external 802.11x devices like the ConnectPort and the Digi Connect Wi-SP, as well as embedded products like the ConnectCore series and Digi Connect series of products. More information on these Digi products can be found at:

http://www.digi.com/products/wireless/wifisolutions/

Specification

XBee Wi-Fi

Dimensions

0.960 x 1.297 (2.438cm x 3.294cm)

Operating Temperature

-40 to 85° C (Industrial)

Antenna Options

PCB Antenna, U.FL Connector, RPSMA Connector, or Integrated Wire

Specifications

General Specifications

XBee® Wi-Fi RF Modules

Specification

XBee Wi-Fi

Frequency

ISM 2.4-2.5GHz

Number of Channels

Channels

1 to 14

Adjustable Power

Yes

Interface immunity

802.11 b, g, and n

Indoor/Urban Range

TBD

Outdoor RF line-of-sight Range

TBD

Transmit Power Output

>15dBm

RF Data Rate

802.11 b 1, 2, 5.5, and 11Mbps

802.11 g 6, 9, 12, 18, 24, 36, 48, and 54 Mbps

802.11 n 6.5, 13, 19.5, 26, 39, 52, 58.5, and 65 Mbps

EVM

802.11 b 1Mbps 8%

802.11 b 2Mbps 17%

802.11 b 5.5Mbps 10%

802.11 b 11Mbps 12%

802.11 g 6Mbps -13dB

802.11 g 9Mbps -15dB

802.11 g 12Mbps -16dB

802.11 g 18Mbps -18dB

802.11 g 24Mbps -19dB

802.11 g 36Mbps -21dB

802.11 g 48Mbps -24dB

802.11 g 54 Mbps -25dB

802.11 n MCS0 6.5Mbps -15dB

802.11 n MCS1 13Mbps -16dB

802.11 n MCS2 19.5Mbps -17dB

802.11 n MCS3 26Mbps -19dB

802.11 n MCS4 39Mbps -20dB

802.11 n MCS5 52Mbps -21dB

802.11 n MCS6 58Mbps -23dB

802.11 n MCS7 65Mbps -24dB

Receiver Sensitivity

802.11 b 1Mbps -97dBm (<8% PER)

802.11 b 2Mbps -93dBm (<8% PER)

802.11 b 11Mbps -89dBm (<8% PER)

802.11 g 6Mbps -91dBm (<10% PER)

802.11 g 54 Mbps -75dBm (<10% PER)

802.11 n 65Mbps -72dBm (<10% PER)

RF Specifications

XBee® Wi-Fi RF Modules

Specification

XBee Wi-Fi

Frequency

ISM 2.4-2.5GHz

Number of

Channels

1 to 14

Adjustable Power

Yes

Interface

immunity

802.11 b, g, and n

Indoor/Urban

Range

TBD

Outdoor RF line-

of-sight Range

TBD

Transmit Power (Average)

802.11 b 1Mbps 16dBm

802.11 b 2Mbps 16dBm

802.11 b 5.5Mbps 16dBm

802.11 b 11Mbps 16dBm

802.11 g 6Mbps 16dBm

802.11 g 9Mbps 16dBm

802.11 g 12Mbps 16dBm

802.11 g 18Mbps 16dBm

802.11 g 24Mbps 15dBm

802.11 g 36Mbps 15dBm

802.11 g 48Mbps 14dBm

802.11 g 54 Mbps 14dBm

802.11 n MCS0 6.5Mbps 16dBm

802.11 n MCS1 13Mbps 16dBm

802.11 n MCS2 19.5Mbps 16dBm

802.11 n MCS3 26Mbps 16dBm

802.11 n MCS4 39Mbps 15dBm

802.11 n MCS5 52Mbps 15dBm

802.11 n MCS6 58Mbps 14dBm

802.11 n MCS7 65Mbps 14dBm

Transmit Power Range (Peak)

802.11b: 11.16 dBm to 19.21 dBm (13.06 mW to 83.37 mW)

802.11g: 13.89 dBm to 20.70 dBm (24.49 mW to 117.49 mW)

802.11n: 14.17dBm to 20.46 dBm (26.12 mW to 111.17 mW) Overall: 11.16 dBm to 20.70 dBm (13.06 mW to 117.49 mW)

RF Data Rate

802.11 b 1, 2, 5.5, and 11Mbps

802.11 g 6, 9, 12, 18, 24, 36, 48, and 54 Mbps

802.11 n 6.5, 13, 19.5, 26, 39, 52, 58.5, and 65 Mbps

EVM

802.11 b 1Mbps 8%

802.11 b 2Mbps 17%

802.11 b 5.5Mbps 10%

802.11 b 11Mbps 12%

XBee® Wi-Fi RF Modules

802.11 g 6Mbps -13dB

802.11 g 9Mbps -15dB

802.11 g 12Mbps -16dB

802.11 g 18Mbps -18dB

802.11 g 24Mbps -19dB

802.11 g 36Mbps -21dB

802.11 g 48Mbps -24dB

802.11 g 54 Mbps -25dB

802.11 n MCS0 6.5Mbps -15dB

802.11 n MCS1 13Mbps -16dB

802.11 n MCS2 19.5Mbps -17dB

802.11 n MCS3 26Mbps -19dB

802.11 n MCS4 39Mbps -20dB

802.11 n MCS5 52Mbps -21dB

802.11 n MCS6 58Mbps -23dB

802.11 n MCS7 65Mbps -24dB

Receiver

Sensitivity

802.11 b 1Mbps -97dBm (<8% PER)

802.11 b 2Mbps -93dBm (<8% PER)

802.11 b 11Mbps -89dBm (<8% PER)

802.11 g 6Mbps -91dBm (<10% PER)

802.11 g 54 Mbps -75dBm (<10% PER)

802.11 n 65Mbps -72dBm (<10% PER)

XBee® Wi-Fi RF Modules

Spectral Mask

XBee Wi-Fi

Data Rate

-50 to 22 MHz

-22 to -11 MHz

11 To 22

Mhz

22 to 50

MHz

Units

802.11 b 1Mbps

-52

-39

-52

dBc

802.11 b 2Mbps

-52

-38

-54

dBc

802.11 b 5.5Mbps

-56

-43

-48

-54

dBc

802.11 b 11Mbps

-54

-39

-37

-55

dBc

Data Rate

-50 to -30 MHz

-30 to -20 MHz

-20 to -11 MHz

-11 to -9 MHz

9 to 11

MHz

11 to 20

MHz

20 to 30

MHz

30 to 50

MHz

Units

802.11 g 6Mbps

-46

-43.5

-28.5

-16.5

-27.5

-42.5

-47

dBc

802.11 g 9Mbps

-46

-42.5

-27.5

-17.5

-16.5

-27.5

-42.5

-46

dBc

802.11 g 12Mbps

-46

-42.5

-28.5

-17.5

-27.5

-41.5

-47

dBc

802.11 g 18Mbps

-46

-42.5

-27.5

-17.5

-27.5

-41.5

-45

dBc

802.11 g 24Mbps

-47

-44.5

-30.5

-19.5

-30.5

-43.5

-47

dBc

802.11 g 36Mbps

-47

-44.5

-30.5

-21.5

-30.5

-46.5

-49

dBc

802.11 g 48Mbps

-47

-48.5

-36.5

-23.5

-24.5

-36.5

-48.5

-52

dBc

802.11 g 54Mbps

-47

-48.5

-33.5

-24.5

-23.5

-33.5

-49.5

-49

dBc

802.11 n MCS0 6.5Mbps

-45

-39.5

-26.5

-16.5

-26.5

-39.5

-45

dBc

802.11 n MCS1 13Mbps

-44

-40.5

-26.5

-16.5

-15.5

-25.5

-39.5

-45

dBc

802.11 n MCS2 19.5Mbps

-44

-41.5

-27.5

-16.5

-27.5

-40.5

-45

dBc

802.11 n MCS3 26Mbps

-44

-40.5

-27.5

-16.5

-25.5

-38.5

-45

dBc

802.11 n MCS4 39Mbps

-45

-42.5

-30.5

-19.5

-29.5

-42.5

-47

dBc

802.11 n MCS5 52Mbps

-46

-43.5

-30.5

-18.5

-29.5

-43.5

-46

dBc

802.11 n MCS6 58Mbps

-47

-45.5

-34.5

-22.5

-33.5

-46.5

-48

dBc

802.11 n MCS7 65Mbps

-47

-46.5

-34.5

-22.5

-33.5

-46.5

-49

dBc

Specification

XBee Wi-Fi

Supply Voltage

3.1 - 3.6 V

Operating Current (transmit, max output power)

802.11 b 1Mbps 260mA

802.11 b 2Mbps 260mA

802.11 b 5.5Mbps 260mA

802.11 b 11Mbps 260mA

802.11 g 6Mbps 240mA

802.11 g 9Mbps 220mA

802.11 g 12Mbps 210mA

802.11 g 18Mbps 200mA

802.11 g 24Mbps 190mA

802.11 g 36Mbps 180mA

802.11 g 48Mbps 170mA

802.11 g 54 Mbps 170mA

802.11 n MCS0 6.5Mbps 230mA

802.11 n MCS1 13Mbps 210mA

802.11 n MCS2 19.5Mbps 200mA

802.11 n MCS3 26Mbps 200mA

802.11 n MCS4 39Mbps 190mA

802.11 n MCS5 52Mbps 180mA

802.11 n MCS6 58Mbps 180mA

802.11 n MCS7 65Mbps 180mA

Operating Current (Receive)

140mA

Deep Sleep Current

<2uA @25C

Electrical Specifications

XBee® Wi-Fi RF Modules

Environmental Specifications

Specification

XBee Wi-Fi

UART Pins

Module Pin Number

DOUT/DIO13

DIN/DIO14

nCTS/DIO7

nRTS/DIO6

Specification

XBee Wi-Fi

SPI Pins

Module Pin Number

SPI_SCLK/DIO2

SPI_SSEL/DIO3

SPI_MOSI/DIO4

SPI_MISO/DIO12

SPI_ATTN/DIO9

Serial Communications Specifications

The XBee Wi-Fi RF modules support both UART (Universal Asynchronous Receiver/Transmitter) and SPI (Serial Peripheral Interface, in master or slave mode) serial connections.

UART

More information on UART operation is found in the UART section in chapter 2.

SPI

The SC2 (Serial Communication Port 2) of the module is connected to the SPI port.

SPI Pin Assignments

XBee® Wi-Fi RF Modules

For more information on SPI operation see the SPI section in chapter 2.

Parameter

Condition

Min

Typ

Max

Units

Input Low Voltage

0.3VDD

Input High Voltage

0.7VDD

Output high Voltage relative to VDD

Sourcing 6mA, VDD=3.0V

95 %

Output low voltage relative to VDD

Sourcing 6mA, VDD=3.0V

5 %

Output fall time

0.5 mA drive strength and load capacitance CL=12.5-25pF.

20+0.1CL

250

2 mA drive strength and load capacitance CL=350-600pF.

20+0.1CL

250

I/O pin hysteresis (VIOTHR+ Viothr-)

VDD=3 to 3.6V

0.1VDD

Pulse width of pulses to be removed by the glitch suppression filter

10 50

GPIO Specifications

The XBee Wi-Fi modules have 14 GPIO (General Purpose Input Output) ports available. Those available will depend on the module configuration as some GPIO’s are consumed by serial communication, etc.

See GPIO section for more information on configuring and using GPIO ports

Electrical Specification for GPIO pads

XBee® Wi-Fi RF Modules

Specification

XBee Wi-Fi

United States (FCC Part 15.247)

FCC ID: MCQ-XBS6

Industry Canada (IC)

IC: 1846A-XBS6

Europe (DC)

ETSI

Australia

Pending

Brazil

Pending

Japan

Pending

Pin #

Name

Direction

Default State

Description

VCC

- - Power Supply

DOUT/DIO13

Both

Output

UART Data out

Din/nConfig/DIO14

Both

Input

UART Data In

DIO12/SPI_MISO

Both

Output

GPIO/ SPI slave out

nRESET

Input

Module Reset

DIO10

Both

GPIO

DIO11

Both

GPIO

reserved

Disabled

Do Not Connect

nDTR/SLEEP_RQ/DIO8

Both

Input

Pin Sleep Control line /GPIO

GND

- - Ground

DIO4/AD4/SPI_MOSI

Both

GPIO/SPI slave In

nCTS/DIO7

Both

Output

Clear-to-Send Flow

Control/GPIO

On_nSLEEP/DIO9/SPI_nATTN

Output

Module Status Indicator/GPIO

VREF

Input - NC

Associate/DIO5

Both

Output

Associate Indicator/GPIO

nRTS/DIO6

Both

Input

Request-to-Send Flow

Control/GPIO

AD3/DIO3/SPI_nSSEL

Both

Analog Input/GPIO/SPI Select

AD2/DIO2/SPI_CLK

Both

Analog Input/GPIO/SPI Clock

AD0/DIO0

Both

Analog Input/GPIO

AD1/DIO1

Both

Analog Input/GPIO

Agency Approvals

FCC Approval (USA) Refer to Chapter 12 FCC Requirements. Systems that contain XBee Wi-Fi modules inherit Digi Certifications.

Pin Signals

Pin Assignment for the XBee Wi-Fi module

(Low‐asserted signals are distinguished with a lower case n before the signal name.)

XBee® Wi-Fi RF Modules

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

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 pin 1 on the PCB as possible. If using a switching regulator for your power supply, switching frequencies above 500 kHz are preferred. Power supply ripple should be limited to a maximum 50mV peak to peak.

Typical start up current for the module is shown in the graph below:

Due to the fast nature of the current peaks, it is recommended that at least a 500uF capacitor be placed on the VCC line. This will enable the XBee to start up with an acceptable voltage slump in the power supply.

Recommended Pin Connections

The only required pin connections are VCC, GND, and either DOUT and DIN or SPI_CLK, SPI_SSEL, SPI_MOSI, and SPI MISO. 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.

Board Layout

The radios are also designed to be self sufficient and work with the integrated and

XBee® Wi-Fi RF Modules

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 pin (pin 15) and the On_nSLEEP pin (pin 13) will change level or behavior based on the state of the module.

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.

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 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.

Antennas should reside above or away from any metal objects like batteries, tall electrolytic capacitors or metal enclosures. Antenna elements radiate perpendicular to the direction they point. Thus a vertical antenna emits across the horizon.

PCB 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 keep out area).

XBee® Wi-Fi RF Modules

Mounting Considerations

XBee modules were designed to mount into a receptacle (socket) and therefore do not require any soldering when mounting to a board. The XBee Wi-Fi Development Kits contain 2 USB interface boards which use two 10-pin receptacles to receive modules.

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.

XBee® Wi-Fi RF Modules

2. RF Module Operation

Serial Communications

The XBee RF Modules interface to a host device through a logic-level asynchronous serial port, or a Serial Peripheral Interface (SPI) port. Through its serial ports, the module can communicate with any logic and voltage compatible UART or SPI; or through a level translator to any serial device (for example: through a RS-232 or USB interface board).

UART Communications

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.

UART Serial Data

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.

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.

XBee® Wi-Fi RF Modules

SPI Communications

The XBee Wi-Fi module supports SPI communications in the slave mode. Slave mode receives the clock signal and data from the master and returns data to the master. The SPI port uses the following signals on the XBee:

 SPI_MOSI (Master Out, Slave In) – inputs serial data from the master  SPI_MISO (Master In, Slave Out) – outputs serial data to the master  SPI_SCLK (Serial Clock) – clocks data transfers on MOSI and MISO  SPI_nSSEL (Slave Select) – enables serial communication with the slave  SPI_nATTN(Attention) – Alerts the master that slave has data queued to send. The XBee module will

assert this pin as soon as data is available to send to the SPI master and it will remain asserted until the SPI master has clocked out all available data.

In this mode the following apply:

 SPI Clock rates up to 3.5 MHz are possible.  Data is MSB first  Frame Format mode 0 is used. This means CPOL=0 (idle clock is low) and CPHA=0 (data is sampled on

the clock’s leading edge). Mode 0 is diagramed below.

 SPI port is setup for API mode and is equivalent to AP=1.

Frame Format for SPI communications

SPI mode is chip to chip communication. Digi does not supply SPI communication option on the Device Development Evaluation Boards.

SPI mode is enabled by holding DOUT/DIO13 (pin 2) low while resetting the module until SPI_nATTN asserts. By this means, the XBee Wi-Fi module will disable the UART and go straight into SPI communication mode. Once configuration is completed, a modem status frame is queued by the module to the SPI port which will cause the SPI_nATTN line to assert. The host can use this to determine that the SPI port has been configured properly. This method internally forces the configuration for the AP, D2, D3, D4, D9, and P2 commands as needed for SPI operations. As long as a WR command is not issued, these configuration values will revert back to previous values after a power on reset. If, on the other hand, a WR command is issued while in SPI mode, these same parameters will be written to flash. It is then the user’s responsibility to set these parameters as appropriate

When the slave select (SPI_nSSEL) signal is asserted by the master, SPI transmit data is driven to the output pin SPI_MISO, and SPI data is received from the input pin SPI_MOSI. The SPI_nSSEL pin has to be asserted to enable the transmit serializer to drive data to the output signal SPI_MISO. A falling edge on SPI_nSSEL causes the SPI_MISO line to be tri-stated such that another slave device can drive it, if so desired..

XBee® Wi-Fi RF Modules

If the output buffer is empty, the SPI serializer transmits the last valid bit repeatedly, which may be either high or low. Otherwise, the module formats all output in API mode 1 format, as described in chapter 7. The attached host is expected to ignore all data that is not part of a formatted API frame.

Serial Buffers

The XBee modules maintain 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 or SPI port

Serial Receive Buffer

When serial data enters the RF module through the DIN Pin (or the MOSI pin), 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 such that the serial receive buffer would overflow, then the new data will be discarded. If the UART is in use, this can be avoided by the host side honoring CTS flow control.

Serial Transmit Buffer

When RF data is received, the data is moved into the serial transmit buffer and sent out the UART or SPI port. If the serial transmit buffer becomes full and system buffers are also full, then the entire RF data packet is dropped. Whenever data is received faster than it can be processed and transmitted out the serial port, there is a potential of dropping data, even in TCP mode.

UART Flow Control

The nRTS and nCTS 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 UAR. RTS and CTS flow control are enabled using the D6 and D7 commands.

XBee® Wi-Fi RF Modules

nCTS Flow Control

The FT command allows the user to specify how many bytes of data can be queued up in the serial transmit buffer before the module asserts CTS low. The serial receive buffer can hold up the 2100 bytes, but FT cannot be set any larger than 2083 bytes, leaving 17 bytes that can be sent by the host before the data is dropped.

By default, FT is 2035 (0x7F3), which allows the host to send 65 bytes to the module after the module asserts CTS before the data is dropped.

In either case, CTS will not be re-asserted until the serial receive buffer has FT-17 or less bytes in use.

nRTS 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 nRTS is de-asserted (set high). The host device should not de-assert nRTS for long 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 RTS flow control is enabled and the XBee is sending data out the UART when nRTS is de-asserted (set high), the XBee could send up to 4 characters out the UART to clear its FIFO after nRTS is de-asserted. This implies that the user needs to de-assert nRTS by the time its receive capacity is within 4 bytes of full.

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 is queued up for RF transmission. When RF data is received, the data is sent out through the UART. The module configuration parameters are configured using the AT command mode interface. Please note that transparent operation is not an option when using SPI.

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

parameter. If RO is zero, data is packetized as soon as it is received, without delay. If RO is non-zero, the data is packetized after RO character times of no transitions on the DIN pin. However, if the time required for RO characters is less than 100 microseconds, then DIN must still be idle for at least 100 microseconds, which is the minimal idle time required for packetizing packets at any baud rate.

 The Command Mode Sequence (GT + CC + GT) is received. Any character buffered in

the serial receive buffer before the sequence is packetized and transmitted before command mode is entered.

 The maximum number of characters that will fit in an RF packet is received.

XBee® Wi-Fi RF Modules

Transparent Operation Features

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.

API Operation Features

Easy to manage data transmissions to multiple destinations

Transmitting RF data to multiple remotes only requires changing the address in the API frame. This Process is much faster than 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

Received data frames indicate the sender's address

All received RF data API frames indicate the source address.

Advanced Networking diagnostics

API frames can provide indication of IO samples from remote devices, transmission status messages, and local radio status messages.

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 UART or SPI is contained in frames that define operations or events within the module.

Transmit Data Frames (received through the DIN pin (pin 3) or SPI_MOSI (pin 11 )) include:

 RF Transmit Data Frame  Local commands (equivalent to AT commands)  Remote commands to be sent to another radio

Receive Data Frames (sent out the DOUT pin (pin 2) or SPI_MISO (pin 4 )) include:

 RF-received data frames  Local command responses  Remote command responses  I/O samples from a remote radio  Event notifications such as transmission status, reset, associate, disassociate, etc.

The API provides an alternative means of configuring modules and of routing data at the local host application layer. A local 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

A Comparison of Transparent and API Operation

The following table compares the advantages of transparent and API modes of operation:

Remote Configuration

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:

If the above conditions do not apply, (e.g. in a sensor node, or a simple application) then transparent operation might be suitable. It is acceptable to use a mixture of devices running API mode and transparent mode in a network.

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:

XBee® Wi-Fi RF Modules

 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

 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  Command Mode (Command Mode Sequence is issued)

Transmit Mode

When serial data is received and is ready to be packetized, the RF module will exit Idle Mode and attempt to transmit the data. The destination address determines which node(s) will receive the data.

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 Operation chapter for an alternate means of configuring modules, which is the only method available for SPI mode. (Command mode is unavailable when using the SPI interface.)

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.]

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