Laird AC4868, AC4868-250 User Manual

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AC4868 868 MHz Transceiver

User’s Guide
Version 2.0

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AC4868 868 MHz Transceiver

Revision

Date

Description

User’s Manual

REVISION HISTORY

1.0 29 August 2005 Initial Release Version

1.1 7 October 2005 Added Declaration of Conformity

1.2 29 May 2007 Updated serial interface section.
Corrected EEPROM write command response.

1.3 18 September 2007 Internal Release

1.4 5 September 2008 Updated to Laird Technologies branding. Clarified Duty Cycle
calculations. Updated information on client to client
communications. Corrected Read Temperature Command to a
max of 0x50. Updated Minimum Baud Rate.

2.0 13 November 2013 Updated to new Laird formatting. General edits.

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AC4868 868 MHz Transceiver

User’s Manual

CONTENTS

Revision History ............................................................................................................................................ 1

Overview....................................................................................................................................................... 5

Features ........................................................................................................................................................ 5

Networking and Security ........................................................................................................................ 5

Easy to Use ............................................................................................................................................ 5

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

Module Specifications ................................................................................................................................ 6

Electrical Specifications ............................................................................................................................... 7

Pin Definitions ............................................................................................................................................ 7

Theory of Operation .................................................................................................................................... 9

RF Architecture ........................................................................................................................................... 9

Modes of Operation ................................................................................................................................... 9

Transmit Mode ...................................................................................................................................... 9

Receive Mode ........................................................................................................................................ 9

Command Mode ................................................................................................................................... 9

Duty Cycle Limitations ............................................................................................................................... 11

European Regulations .............................................................................................................................. 11

Radio Operation ....................................................................................................................................... 11

Transmit Calculations ........................................................................................................................... 11

Serial Interface ........................................................................................................................................... 12

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

Asynchronous Operation ..................................................................................................................... 12

Parity ................................................................................................................................................... 12

OEM Host Data Rate ................................................................................................................................ 13

Serial Interface Baud Rate ......................................................................................................................... 13

Interface Timeout / RF Packet Size ............................................................................................................ 13

Flow Control ............................................................................................................................................ 14

Half Duplex / Full Duplex .......................................................................................................................... 14

System Timing and Latency ...................................................................................................................... 15

System Throughput .................................................................................................................................. 15

Software Interface ..................................................................................................................................... 16

Networking .............................................................................................................................................. 16

Range Refresh .......................................................................................................................................... 16

Auto Config Parameters ........................................................................................................................... 16

Max Power ............................................................................................................................................... 17

Timing Diagrams ........................................................................................................................................ 18

AC 4868-250 Timing Diagrams ................................................................................................................ 18

Hardware Interface .................................................................................................................................... 20

Pin Definitions .......................................................................................................................................... 20

Generic I/O .......................................................................................................................................... 20

TXD and RXD ....................................................................................................................................... 20

Hop Frame ........................................................................................................................................... 20

CTS ...................................................................................................................................................... 20

GND .................................................................................................................................................... 20

RTS ...................................................................................................................................................... 20

Test / 9600 Baud .................................................................................................................................. 21

UP_Reset ............................................................................................................................................. 21

Command / Data ................................................................................................................................. 21

AD In and DA Out ................................................................................................................................ 21

In Range .............................................................................................................................................. 21

Configuring the AC4868-250 .................................................................................................................... 22

AT Commands ......................................................................................................................................... 22

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AC4868 868 MHz Transceiver

User’s Manual

On-the-Fly Control Commands ............................................................................................................ 23

Command Descriptions ............................................................................................................................ 24

Enter AT Command Mode ................................................................................................................... 24

Exit AT Command Mode ...................................................................................................................... 24

Status Request ..................................................................................................................................... 24

Change Server / Client ......................................................................................................................... 25

Sleep Walk Power-Down ..................................................................................................................... 25

Sleep Walk Power-Down Wake Up ...................................................................................................... 25

Broadcast Packets ................................................................................................................................ 25

Write Destination Address ................................................................................................................... 26

Read Destination Address .................................................................................................................... 26

Auto Destination .................................................................................................................................. 26

Read Digital Inputs ............................................................................................................................... 26

Read ADC ............................................................................................................................................ 27

Write Digital Outputs ........................................................................................................................... 27

Write DAC ........................................................................................................................................... 27

Set Max Power ..................................................................................................................................... 28

Transmit Buffer Empty ......................................................................................................................... 28

Deep Sleep Mode ................................................................................................................................ 28

Read Temperature ............................................................................................................................... 28

EEPROM Byte Read .............................................................................................................................. 28

EEPROM Byte Write ............................................................................................................................. 29

Reset ................................................................................................................................................... 29

EEPROM Parameters .................................................................................................................................. 30

Dimensions ................................................................................................................................................. 33

Mechanical Drawings ............................................................................................................................... 33

Ordering Information ................................................................................................................................ 34

Product Part Number Tree ........................................................................................................................ 34

Developer Kit Part Numbers ..................................................................................................................... 34

Compliancy Information ............................................................................................................................ 35

Agency Identification Numbers ................................................................................................................. 35

Approved Antenna List ............................................................................................................................. 35

OEM Equipment Labeling Requirements ................................................................................................... 35

Country Restrictions ................................................................................................................................. 36

Country Notification ................................................................................................................................. 36

Declaration of Conformity ........................................................................................................................ 37

Appendix I: Sample Power Supply ............................................................................................................ 38

Bill of Materials ........................................................................................................................................ 38

Schematic ................................................................................................................................................ 39

PCB Layout ............................................................................................................................................... 39

Appendix II: 5V to 3.3V Levels .................................................................................................................. 41

Voltage Level Conversion ICs .................................................................................................................... 41

Passive Resistor Voltage Divider ................................................................................................................ 41

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AC4868 868 MHz Transceiver

User’s Manual

OVERVIEW

The compact AC4868-250 868MHz transceiver can replace miles of cable in
harsh industrial environments. Using field-proven technology which needs
no additional CE licensing in Europe, OEMs can easily make existing systems
wireless with little or no RF expertise.

The AC4868-250 is a member of Laird Technologies’s ConnexRF OEM
transceiver family. The AC4868-250 is designed for integration into OEM
systems operating under European ETSI regulations for the 868 - 870 MHz
band.

AC4868-250 transceivers provide an asynchronous TTL/RS-485 level serial
interface for OEM Host communications. Communications include both
system and configuration data. The Host supplies system data for transmission to other Host(s). Configuration
data is stored in the on-board EEPROM. All synchronization and RF system data transmission/reception is
performed by the transceiver.

AC4868-250 transceivers can operate in a Point-to-Point, Point-to-Multipoint, or Peer-to-Peer architecture.
The AC4868-250 utilizes a single channel synchronization allowing all radios to communicate with any radio
in range. Optionally any radio can be configured as a Server to provide a synchronization beacon. This beacon
is used by the Client radios to determine In Range status and for Auto Destination addressing.

This document contains information about the hardware and software interface between a Laird Technologies
AC4868-250 transceiver and an OEM Host. Information includes the theory of operation, specifications,
interface definition, configuration information and mechanical drawings. The OEM is responsible for ensuring
the final product meets all appropriate regulatory agency requirements listed herein before selling any
product.

Note: Unless mentioned specifically by name, the AC4868-250 modules will be referred to as the “radio”

or “transceiver”. Individual naming is used to differentiate product specific features. The host
(PC/Microcontroller/Any device to which the AC4868-250 module is connected) will be referred to
as “OEM Host”.

FEATURES

Networking and Security

 Drop-in replacement for AC4490 900

MHz & AC4424 2.4 GHz product
families

 Generic I/O digital lines and integrated

DAC/ADC functions

 Retries and Acknowledgements
 Low latency and high throughput

Easy to Use

 Software selectable interface baud rates from 1200 bps

to 57.6 kbps

 Low cost, low power and small size ideal for high

volume, portable and battery powered applications

 All modules are qualified for Industrial temperatures

(-40°C to 80°C)

 Advanced configuration available using AT commands
 Server/Client or peer-to-peer communication

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AC4868 868 MHz Transceiver

Parameter

Description

Parameter

Description

Parameter

Description

User’s Manual

SPECIFICATIONS

Module Specifications

Table 1: General Specifications

20 Pin Interface Connector Molex 87759-0030, mates with Samtec SMM-110-02-S-D

RF Connector Telegartner J01341C0081, mates with any manufacturer’s MMCX style plug

Antenna AC4868-250: MMCX Connector

Serial Interface Data Rate Baud rates from 1200 bps to 57.6 kbps

Power Consumption
(typical)

Channels Single Channel

Security One byte System ID. 56-bit DES encryption key.

Interface Buffer size Input/Output:256 bytes each

Physical Dimensions Transceiver with MMCX Connector: 1.65” x 1.9” x 0.20”

10% TX 50% TX 100% TX 100% RX Pwr-Down Deep Sleep

54 mA 138 mA 240 mA 36 mA TBD 24 mA

Table 2: Transceiver Specifications

Frequency Band Europe 500 mW: 869.4 - 869.65 MHz

RF Data Rate 19.2 kbps or 28.8 kbps dependent on interface baud rate

RF Technology Single Frequency FSK

Output Power

Conducted (no antenna) EIRP (2.5 dBi gain antenna)

186 mW typical 250 mW typical

Supply Voltage Pin 10 (uP power): 3.3 – 5.5V ±50mV ripple; draws ~30-50mA. Must be connected.

Pin 11 (PA power): 3.3 ±3%, ±100mV ripple; draws most current. Must be connected.

Sensitivity -103dBm typical @ 28.8kbps RF Data Rate

EEPROM write cycles 20000

Hop period 53 ms

Range, Line of Sight

Up to 15 km (9.3 miles)

(2.5dBi gain ant.)

Table 3: Environmental Specifications

Operating Temp -40˚C to +80˚C

Storage Temp -50˚C to +85˚C

Humidity (non-condensing) 10% to 980%

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AC4868 868 MHz Transceiver

Signal Name

Module Pin

Type

High Min.

Low Max.

Unit

Pin #

Type

Signal Name

Function

Note

Signal Name

High Min.

High Max.

Low Min.

Low Max.

Unit

User’s Manual

Electrical Specifications

Table 4: Input Voltage Characteristics

RS485 A/B N/A 12 -7 N/A V

RXD 2.31 3.3 0 0.99 V

GI0 2.31 3.3 0 0.99 V

RTS 2.31 3.3 0 0.99 V

TEST

GI1 2.31 3.3 0 0.99 V

UP_Reset 0.8 3.3 0 0.6 V

Command/Data 2.31 3.3 0 0.99 V

AD In N/A 3.3 0 N/A V

Table 5: Output Voltage Characteristics

GO0 1 O 2.5 @ 8mA 0.4 @ 8mA V

TXD 2 O 2.5 @ 2mA 0.4 @ 2mA V

RS485 A/B 2,3 I/O 3.3 @ 1/8 Unit Load N/A V

CTS 7 O 2.5 @ 2mA 0.4 @ 2mA V

GO1

DA_Out 19 O N/A N/A V

In_Range 20 O 2.5 @ 2mA 0.4 @ 2mA V

2.31 3.3 0 0.99 V

8 O 2.5 @ 2mA 0.4 @ 2mA V

Pin Definitions

1 O GO0 Generic Output pin

2 O TXD Transmitted data out of the transceiver

I/O RS485 A (true) Non-inverted RS-485 representation of serial data

3 I RXD Data input to the transceiver

I/O RS485 B (Invert) Mirror image of RS-485 A

4 I GI0 Generic Input pin

5,16 GND GND Signal Ground

6 N/C This pin has an internal connection and should be left disconnected.

7 O CTS Clear to Send – Active Low when the transceiver is ready to accept data

for transmission.

8 I RTS Request to Send – When enabled in EEPROM, the OEM Host can take

this High when it is not ready to accept data from the transceiver.

: Keeping RTS High for too long can cause data loss.

9 O GO1 Generic Output pin

10 PWR VCC1 3.3 – 5.5V, ±50mV ripple. Powers the radio’s uP. Draws ~30-50mA.

11 PWR VCC2 3.3V, ±50mV ripple. Powers the radio’s power amplifier. Current draw

depends on duty cycle and output power.

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AC4868 868 MHz Transceiver

User’s Manual

12 I Test Test Mode – When pulled logic Low and then applying power or

resetting, the transceiver’s serial interface is forced to a 9600, 8-N-1 rate.
To exit, the transceiver must be reset or power-cycled with Test Mode
logic High.

13 N/C This pin has an internal connection and should be left disconnected.

14 I GI1 Generic Input pin

15 I UP_RESET RESET – Controlled by the AC4868-250 for power-on reset if left

unconnected. After a stable power-on reset, a logic High pulse will reset
the transceiver.

17 I CMD?Data When logic Low, the transceiver interprets OEM Host data as command

data. When logic High, the transceiver interprets OEM Host data as
transmit data.

18 I AD In 10 bit Analog Data Input

19 O DA_Out 10 bit Analog Data Output

20 O In_Range When logic Low, a Client is in range of a Server on same Channel and

System ID. Always low on a Server.

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AC4868 868 MHz Transceiver

User’s Manual

THEORY OF OPERATION

RF Architecture

The AC4868-250 is a single channel radio transceiver. Each unit can be configured as a Server or as a Client.
Servers are responsible for sending out beacons and for allow for radios to be configured very simply in a
point-to-multipoint network. Servers are not required for operation, but if they are used, there should only be
one Server per network. All other radios in the network should be configured as Clients. Clients can
communicate point-to-point or in a mesh with or without a Server.

Modes of Operation

The AC4868-250 has three different operating modes; Receive, Transmit, & Command Mode. If the
transceiver is not communicating with another radio, it will be in Receive Mode actively listening for a beacon
from the Server. If the Client determines that the beacon is from a server operating on the same RF Channel
and System ID, it will respond by asserting In_Range Low. A transceiver will enter Transmit or Command mode
when the OEM Host sends data over the serial interface. The state of the Command/Data pin (Pin 17) or the
data contents determine which of the two modes will be entered.

Transmit Mode

All packets sent over the RF are either Addressed or Broadcast packets. Broadcast and Addressed delivery can
be controlled dynamically with the API Control byte and corresponding on-the-fly commands. To prohibit
transceivers from receiving broadcast packets, Unicast only can be enabled.

Addressed Packets

When sending an addressed packet, the RF packet is sent only to the receiver specified in destination address.
To increase the odds of successful delivery, Transmit retries are utilized. transparent to the OEM Host; the
sending radio will send the RF packet to the intended receiver. If the receiver receives the packet free of errors,
it will return an RF acknowledge within the same 53 ms hop. If a receive acknowledgement is not received, the
radio will use a transmit retry to resend the packet. The radio will continue sending the packet until either (1)
an acknowledgement is received or (2) all transmit retries have been used. The received packet will only be
sent to the OEM Host if and when it is received free of errors.

Broadcast Packets

When sending a broadcast packet, the RF packet is sent out to every eligible transceiver on the network. To
increase the odds of successful delivery, Broadcast attempts are utilized. Transparent to the OEM Host, the
sending radio will send the RF packet to the intended receiver(s). Unlike transmit retries, all broadcast attempts
are used; regardless of when the RF packet is actually received and without RF acknowledgements. If the
packet is received on the first attempt, the receiver will ignore the remaining broadcast attempts. The received
packet will only be sent to the OEM Host if and when it is received free of errors.

Receive Mode

When a transceiver is not in Transmit or Command mode, it will be in Receive Mode listening for data. While
in Receive Mode, subsequent data of up to 80 bytes can be received every hop (53 ms).

Command Mode

A radio will enter Command Mode when data is received over the serial interface from the OEM Host and
either the Command/Data pin (pin 17) is logic Low or the received data contains the “AT+++” (Enter AT

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AC4868 868 MHz Transceiver

User’s Manual

Command Mode) command. Once in Command Mode, all data received by the radio is interpreted as
command data. Command Data can be either EEPROM Configuration or On-The-Fly commands.

Figure 1: Pending RF and Data in Buffer Flow

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AC4868 868 MHz Transceiver

RF Baud Rate

Addressed Mode

RF Packet Size

User’s Manual

DUTY CYCLE LIMITATIONS

European Regulations

ETSI requirements as specified in the ETSI EN 300 220-1 define the requirements for the 868-870MHz bands.
For a conducted output of 180mW and radiated outputs up to 500mW, the maximum allowed duty cycle is
<10%. This duty cycle is measured as the amount of TX time on, monitored over one hour and relative to a
one hour period. Thus for the AC4868-250, the maximum “on” time in an hour cannot exceed six minutes.

Radio Operation

The AC4868 will transmit data whenever data is present on the serial UART. Data will be transmitted for
Broadcast packets according to the value of the Broadcast Attempts. For Addressed Packets data will be
transmitted until a successful acknowledgement is received. The OEM is responsible for limiting the
Transmitter’s “on” time to less than the duty cycle regulations.

Transmit Calculations

For a rough estimate the TX Time on is 53ms * the number of retries or attempts. By default this is 212ms. For
servers you need to a 5ms beacon.

The interval time is based on an increment of data equal to or less than the packet size given in Table 6.

Table 6: RF Packet Size

19200 Addressed 0x24

28800 Addressed 0x50

19200 Broadcast 0x40

28800 Broadcast 0x60

So the total TX On Time is 5ms (For Servers) + Data Size/RF Packet Size * Number of Retries/Attempts.

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AC4868 868 MHz Transceiver

User’s Manual

SERIAL INTERFACE

In order for the OEM Host and a transceiver to communicate over the serial interface they need to have the
same serial data rate. Refer to the following sections to ensure that the OEM Host data rate matches the serial
interface baud rate.

Serial Communications

The AC4868-250 is a TTL device which can be interfaced to a compatible UART (microcontroller) or level
translator to allow connection to serial devices. UART stands for Universal Asynchronous Receiver Transmitter
and its main function is to transmit or receive serial data.

Asynchronous Operation

Since there is no separate clock in asynchronous operation, the receiver needs a method of synchronizing with
the transmitter. This is achieved by having a fixed baud rate and by using START and STOP bits. A typical
asynchronous mode signal is shown below.

Figure 2: Asynchronous Mode Signal

The UART outputs and inputs logic level signals on the TX and RX pins. The signal is high when no data is
being transmitted and goes low when transmission begins.

The signal stays low for the duration of the START bit and is followed by the data bits; LSB first. The STOP bit
follows the last data bit and is always high. After the STOP bit has completed, the START bit of the next
transmission can occur.

Parity

A parity bit is used to provide error checking for a single bit error. When a single bit is used, parity can be
either even or odd. Even parity means that the number of ones in the data and parity sum to an even number
and vice-versa. The ninth data bit can be used as a parity bit if the data format requires eight data bits and a
parity bit as shown below.

Figure 3: Even Parity Bit

Note: Enabling parity cuts throughput and the interface buffer in half.

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AC4868 868 MHz Transceiver

Data Bits

Parity*

Stop Bits

Transceiver Programming Requirements

Baud

BaudL
(0x42)

BaudH
(0x43)

RF Baud (not
adjustable)

Minimum Interface
Timeout (0x58)

Stop Bit Delay
(0x3F)

1

User’s Manual

OEM Host Data Rate

The OEM Host Data Rate is the rate with which the OEM Host and transceiver communicate over the serial
interface. Possible values range from 1200 bps to 57,600 bps.

Note: Enabling Parity cuts throughput in half and the Interface Buffer size in half. Table 7 shows the

supported asynchronous serial data formats.

Table 7: Supported Serial Formats

8 N 1 Parity Disabled

7 N 2 Parity Disabled

7 E,O,M,S 1 Parity Disabled

9 N 1 Parity Enabled

8 N 2 Parity Enabled

8 E,O,M,S 1 Parity Enabled

7 E,O,M,S 2 Parity Enabled

*Mark (M) corresponds to 1 & Space (S) corresponds to 0

Serial Interface Baud Rate

This two-byte value determines the baud rate used for communicating over the serial interface to a
transceiver. The Table below lists values for some common baud rates. Baud rates below 1200 and above
57600 baud are not supported. For a baud rate to be valid, the calculated baud rate must be within ±3% of
the OEM Host baud rate. If the Test pin (Pin 12) is pulled logic Low at reset, the baud rate is forced to 9600.

57600

0xFC 0x00 28800 0x02 0x03

38400 0xFA 0x00 19200 0x02 0x08

28800 0xF8 0x00 28800 0x02 0x0E

19200 0xF4 0x00 19200 0x03 0x19

14400 0xF0 0x00 28800 0x04 0x23

9600 0xE8 0x00 19200 0x05 0x39

1. 57600 is the default baud rate.

Interface Timeout / RF Packet Size

Interface Timeout (EEPROM address 0x58), in conjunction with RF Packet Size (EEPROM address 0x5B),
determines when a buffer of data will be sent out over the RF as a complete RF packet, based on whichever
condition occurs first.

Interface Timeout – Interface Timeout specifies a maximum byte gap between consecutive bytes. When that
byte gap is exceeded, the bytes in the transmit buffer are sent out over the RF as a complete packet. Interface
Timeout is adjustable in 0.5ms increments and has a tolerance of ±0.5ms. Therefore, the Interface Timeout
should be set to a minimum of 2. The default value for Interface Timeout is 0x04 (2ms) and should be adjusted
accordingly when changing the transceiver baud rate.

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