Laird AC4868 User manual

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AC4868 868 MHz Transceiver
User’s Guide
Version 2.0

AC4868 868 MHz Transceiver
User’s Manual
Americas: [phone] Option 3 2 Laird Technologies
Europe: [phone]
Hong Kong: [phone]
www.lairdtech.com/ramp
REVISION HISTORY
Revision
Date
Description
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.

AC4868 868 MHz Transceiver
User’s Manual
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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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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

AC4868 868 MHz Transceiver
User’s Manual
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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

AC4868 868 MHz Transceiver
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SPECIFICATIONS
Module Specifications
Table 1: General Specifications
Parameter
Description
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)
10% TX 50% TX 100% TX 100% RX Pwr-Down Deep Sleep
54 mA 138 mA 240 mA 36 mA TBD 24 mA
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”
Table 2: Transceiver Specifications
Parameter
Description
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
(2.5dBi gain ant.)
Up to 15 km (9.3 miles)
Table 3: Environmental Specifications
Parameter
Description
Operating Temp -40˚C to +80˚C
Storage Temp -50˚C to +85˚C
Humidity (non-condensing) 10% to 980%

AC4868 868 MHz Transceiver
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Electrical Specifications
Table 4: Input Voltage Characteristics
Table 5: Output Voltage Characteristics
Signal Name
Module Pin
Type
High Min.
Low Max.
Unit
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 8 O 2.5 @ 2mA 0.4 @ 2mA V
DA_Out 19 O N/A N/A V
In_Range 20 O 2.5 @ 2mA 0.4 @ 2mA V
Pin Definitions
Pin #
Type
Signal Name
Function
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.
Note
: 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.
Signal Name
High Min.
High Max.
Low Min.
Low Max.
Unit
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 2.31 3.3 0 0.99 V
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

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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.

AC4868 868 MHz Transceiver
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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

AC4868 868 MHz Transceiver
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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