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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AC4868 868 MHz Transceiver

User’s Manual

RF Packet Size – When the number of bytes in the transceiver transmit buffer equals RF Packet Size, those
bytes are sent out as a complete RF packet. It is much more efficient to send a few large packets rather than
several short packets as every packet the transceiver sends over the RF contains extra header bytes which are
not included in the RF Packet Size. However, if the RF Packet Size is set too large, the transceiver will not be
able to send any packets because the AC4868 requires the entire RF packet to be sent in the same hop period
(53 ms). The RF packet size if programmed in EEPROM automatically when Auto Config is enabled. It is
strongly recommended that Auto Config be left enabled to maximize the efficiency of the transceiver. RF
Packet Size must be set to a minimum of 6 in order to send the Enter AT command.

Flow Control

Flow control refers to the control of data flow between transceivers. It is the method used to handle data in
the transmit/receive buffer and determines how data flow between the transceivers is started and stopped.
Often, one transceiver is capable of sending data much faster than the other can receive and flow control
allows the slower device to tell the faster device when to pause and resume data transmission.

Engineer’s Tip: Can I implement a design using just Txd, Rxd and Gnd (Three-wire Interface)?

Yes. However, it is strongly recommended that your hardware monitor the CTS pin of the

radio. CTS is taken High by the radio when its interface buffer is getting full. Your hardware
should stop sending at this point to avoid a buffer overrun (and subsequent loss of data).

You can perform a successful design without monitoring CTS. However, you need to take

into account the amount of latency the radio adds to the system, any additional latency
caused by Transmit Retries or Broadcast Attempts, how often you send data, non-delivery
network timeouts and interface data rate. Polled type networks, where the Server host
requests data from the Client host and the Client host responds, are good candidates for
avoiding the use of CTS. This is because no one transceiver can monopolize the RF link.
Asynchronous type networks, where any radio can send to another radio at any point in
time, are much more difficult to implement without the use of CTS.

Half Duplex / Full Duplex

When Half Duplex communication is chosen, the AC4868-250 will send a packet out over the RF whenever it
can. This can cause packets sent by multiple transceivers at the same time to collide with each other over the
RF. To prevent this, Full Duplex communication can be chosen. Full Duplex shares the bandwidth intelligently
to enable two-way collision-free communication without any collision. This is done by calculating the amount
of time until the next hop to ensure that it has time to send the packet; if there is enough time, it will send the
packet and if not, it will wait until its next appropriate hop. The Server transmits during the even hops while
the Client(s) will transmit during the odd hops. Although there is technically only one frequency bin, the Server
still maintains a bin count for the purpose of handling Full Duplex mode. While the RF hardware is still
technically half duplex, the bandwidth sharing it makes the transceiver seem full duplex. Enabling Full Duplex
can cause overall throughputs to be cut in half.

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AC4868 868 MHz Transceiver

RF Mode

RF Baud (determined by
interface baud)

Half Duplex Throughput
(bps)

Full Duplex Throughput
(bps) each way

User’s Manual

System Timing and Latency

Care should be taken when selecting transceiver architecture, as it can have serious effects on data rates,
latency, and overall system throughput. The importance of these three characteristics will vary from system to
system and should be a strong consideration when designing the system.

Engineer’s Tip: In High-density applications, what amount of latency should be expected?

It is not easy to predict the exact amount of latency in high-density applications. There are

many variables that affect system latency. The three variables that most affect the latency
are the network load, the distance between transceivers, and whether the transceivers are
operating in a broadcast or addressed mode. There is no fixed answer as to how much
latency will be introduced in the system when considering high-density applications. In
these cases we can just offer qualitative analysis of the latency in high-density applications.
As the network load increases, then the number of collisions that will occur increases. As
the number of collisions increase, then the system latency increases. As the distance
between the transceivers increases, so to does the system latency. Finally, when
transceivers operate in addressed mode they will retry sending a packet up to the number
of time specified in the transmit retry parameter specified in the EEPROM. As the number
of retries increases, the system latency will increase also.

System Throughput

When operating as shown below, an AC4868-250 transceiver is capable of achieving the listed throughput.
However, in the presence of interference or at longer ranges, the transceiver may be unable to meet the
specified throughput.

Table 8: Maximum system throughput

Addressed 28800 15k 7.5k

Addressed 19200 6.8k 3.4k

Addressed 28800 18k 9k

Addressed 19200 12k 6k

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AC4868 868 MHz Transceiver

RF Channel Number
Range (0x40)

Frequency Details & Regulatory requirements

Countries
Parameter

EEPROM Address

Default

RF Baud = 19200

RF Baud = 28800

Addressed

Broadcast

Addressed

Broadcast

User’s Manual

SOFTWARE INTERFACE

Networking

System ID - System ID (EEPROM address 0x76) is similar to a password character or network number and
makes network eavesdropping more difficult. A transceiver will not establish a Session or communicate with a
transceiver operating on a different System ID or Channel Number.

RF Channel Number – See Table 9.

Table 9: RF Channel Number Settings

0x38 869.4 - 869.65 MHz (Single Frequency. Up to 500 mW

EIRP @ 10% maximum transmit vs. receive duty cycle

DES (Data Encryption Standard) - DES (Data Encryption Standard) – Encryption is the process of encoding an
information bit stream to secure the data content. The DES algorithm is a common, simple and
well-established encryption routine. An encryption key of 56 bits is used to encrypt the packet. The receiver
must use the exact same key to decrypt the packet; otherwise garbled data will be produced.

To enable DES, EEPROM Byte 0x45, bit 6 must be set to a value of 1. To disable DES, set bit 6 to a value of 0.
The 7 byte (56 bits) Encryption/Decryption Key is located in EEPROM Bytes 0xD0 – 0xD6.

Note: It is highly recommended that this Key be changed from the default.

Europe

Range Refresh

Range Refresh - Range Refresh specifies the maximum amount of time a Client reports in range without
having heard a beacon from the Server. Each time the Client hears a beacon, it resets its Range Refresh timer.
If the timer reaches zero, the Client will go out of range, take its In_Range pin High and enter acquisition
mode attempting to find the Server once again. The range refresh is equal to the hop period (53 ms) x Range
refresh value.

Note: Range Refresh should not be set to 0x00.

Auto Config Parameters

The AC4868-250 has several variables that vary by RF mode and architecture. By default, Auto Config is
enabled and bypasses the values stored in EEPROM and uses predetermined values for the given operating
mode. Below is a list of the variables controlled by Auto Config and their respective predetermined values. If
Auto Config is disabled, these values must be programmed in the transceiver EEPROM for the corresponding
mode of operation.

Table 10: Auto COnfig Parameters

RF Packet Size 0x5B 0x24 0x24 0x40 0x50 0x60

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AC4868 868 MHz Transceiver

User’s Manual

Max Power

Max Power provides a means for controlling the RF output power of the AC4868. Output power and current
consumption can vary by as much as ±10% per transceiver for a particular Max Power setting. Contact Laird
Technologies for assistance in adjusting Max Power.

Engineer’s Tip: The max power is set during Production and may vary slightly from one transceiver to

another. The max power can be set as low as desired but should not be set above the original
factory setting. A backup of the original power setting is stored in EEPROM address 0x8E.

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AC4868 868 MHz Transceiver

User’s Manual

TIMING DIAGRAMS

AC 4868-250 Timing Diagrams

Figure 4: Addressed Mode with Timeout

Figure 5: Addressed Mode with Fixed Packet Length

Figure 6: Broadcast Mode with Timeout

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AC4868 868 MHz Transceiver

User’s Manual

Figure 7: Broadcast mode with Fixed Packet Length

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AC4868 868 MHz Transceiver

User’s Manual

HARDWARE INTERFACE

Below is a description of all hardware pins used to control the AC4868-250.

Pin Definitions

Generic I/O

Both GIn pins serve as generic input pins and both GOn pins server as generic output pins. Reading and
writing of these pins can be performed using CC Commands.

TXD and RXD

Serial TTL

The AC4868-250 accepts 3.3VDC TTL level asynchronous serial data on the RXD pin and interprets that data
as either Command Data or Transmit Data. Data is sent from the transceiver, at 3.3V levels, to the OEM Host
via the TXD pin.

RS-485

When equipped with an onboard RS-485 interface chip, TXD and RXD become the half duplex RS-485 pins.
The transceiver interface will be in Receive Mode except when it has data to send to the OEM Host. TXD is the
noninverted representation of the data (RS485A) and RXD is a mirror image of TXD (RS485B). The transceiver
will still use RTS (if enabled).

Hop Frame

Transitions logic Low at the start of a hop and transitions logic High at the completion of a hop. The OEM Host
is not required to monitor Hop Frame. The AC4868 is a single frequency radio that uses fictitious hops, though
it generates a Hop Frame signal every time it transmits a timing beacon.

CTS

The AC4868-250 has an interface buffer size of 256 bytes. If the buffer fills up and more bytes are sent to the
transceiver before the buffer can be emptied, data loss will occur. The transceiver prevents this loss by
asserting CTS High as the buffer fills up and taking CTS Low as the buffer is emptied. CTS On and CTS Off
control the operation of CTS. CTS On specifies the amount of bytes that must be in the buffer for CTS to be
disabled (logic High). Even while CTS is disabled, the OEM Host can still send data to the transceiver, but it
should do so carefully.

Note: The CTS On/Off bytes of the EEPROM can be set to 1, in which case CTS will go high as data is sent

in and low when buffer is empty.

GND

Signal Ground. Pins are internally connected.

RTS

With RTS disabled, the transceiver will send any received data to the OEM Host as soon as it is received.
However, some OEM Hosts are not able to accept data from the transceiver all of the time. With RTS enabled,

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AC4868 868 MHz Transceiver

User’s Manual

the OEM Host can prevent the transceiver from sending it data by disabling RTS (logic High). Once RTS is
enabled (logic Low), the transceiver can send packets to the OEM Host as they are received.

Note: Leaving RTS disabled for too long can cause data loss once the transceiver’s 256 byte receive buffer

fills up.

Test / 9600 Baud

When pulled logic Low before applying power or resetting, the transceiver’s serial interface is forced to a
9600, 8-N-1 (8 data bits, No parity, 1 stop bit). To exit, the transceiver must be reset or power-cycled with Test
pin logic High. This pin is used to recover transceivers from unknown baud rates only. It should not be used in
normal operation. Instead the transceiver Interface Baud Rate should be programmed to 9600 baud if that
rate is desired for normal operation.

Engineer’s Tip: Laird Technologies does not recommend permanently grounding the Forced_9600 pin.

This mode was intended for recovering transceivers from unknown settings and was not
intended for use in real-time communications.

UP_Reset

UP_Reset provides a direct connection to the reset pin on the AC4868-250 microprocessor and is used to
force a soft reset. For a valid reset, reset must be asserted High for a minimum of 11ms.

Command / Data

When logic High, the transceiver interprets incoming OEM Host data as transmit data to be sent to other
transceivers and their OEM Hosts. When logic Low, the transceiver interprets OEM Host data as command
data.

AD In and DA Out

AD In & DA Out can be used as a cost savings to replace Analog-to-Digital and Digital-to-Analog converter
hardware. Read this pin locally with the Read ADC command in the On-the-Fly Control Command Reference.
DA Out is an unbuffered, high impedance output and MUST be buffered by the OEM Host when used.

In Range

Reports logic Low when a Client transceiver is in range of a Server radio operating on the same RF Channel
and system ID. If a Client cannot hear a Server for the amount of time defined by Range Refresh, it will drive
In_Range High and enter search mode looking for a Server. When a server is detected, In_Range will be
asserted Low. In_Range will always report Low on Server transceivers.

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AC4868 868 MHz Transceiver

User’s Manual

CONFIGURING THE AC4868-250

The AC4868-250 can be configured using the CC Configuration Commands. The CC Commands can be
issued using either Hardware or Software Configuration. To use Hardware Configuration, pin 17 of a
transceiver must be asserted Low. Software Configuration can be used by entering AT Command Mode
before issuing the CC Commands.

Figure 8: AC5868-250 Configuration Flow

AT Commands

The AT Command mode implemented in the AC4868-250 creates a virtual version of the Command/Data pin.
The “Enter AT Command Mode” Command asserts this virtual pin Low (to signify Command Mode) and the
“Exit AT Command Mode” Command asserts this virtual pin High (to signify Data). Once this pin has been
asserted Low, all On-the-Fly CC Commands documented in the manual are supported.

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AC4868 868 MHz Transceiver

Command Name

Command (All bytes in Hex)

Return (All bytes in hex)

User’s Manual

On-the-Fly Control Commands

The AC4868-250 transceiver contains static memory that holds many of the parameters that control the
transceiver operation. Using the “CC” command set allows many of these parameters to be changed during
system operation. Because the memory these commands affect is static, when the transceiver is reset, these
parameters will revert back to the settings stored in the EEPROM. While in CC Command mode using pin 17
(Command/Data), the RF interface of the transceiver is still active. Therefore, it can receive packets from
remote transceivers while in CC Command mode and forward these to the OEM Host.

While in CC Command mode using AT Commands, the RF interface of the transceiver is active, but packets
sent from other transceivers will not be received. The transceiver uses Interface Timeout/RF Packet Size to
determine when a CC Command is complete. Therefore, there should be no delay between each character as
it is sent from the OEM Host to the transceiver or the transceiver will not recognize the command. If the OEM
Host has sent a CC Command to the transceiver and an RF packet is received by the transceiver, the
transceiver will send the CC Command response to the OEM Host before sending the packet. However, if an
RF packet is received before the Interface Timeout expires on a CC Command, the transceiver will send the
packet to the OEM Host before sending the CC Command response.

When an invalid command is sent, the radio scans the command to see if it has a valid command followed by
bytes not associated with the command, in which case the radio discards the invalid bytes and accepts the
command. In all other cases, the radio returns the first byte of the invalid command back to the user and
discards the rest.

Enter AT Command
Mode

Exit AT Command
Mode

Status Request 0xCC 0x00 0x00 - - - 0xCC Firmware

Change Server / Client 0xCC 0x03 0x00: Server

Sleep Walk Power
Down

Sleep Walk Wake Up 0xCC 0x07 - - - - 0xCC Channel - -

Broadcast Packets 0xCC 0x08 0x00: Broadcast

Write Destination
Address

Read Destination
Address

Auto Destination 0xCC 0x15 Bit 0: Auto Destination

Read Digital Inputs 0xCC 0x20 - - - - 0xCC Bit 0: GO0

Read ADC 0xCC 0x21 0x01: AD in

Write Digital Outputs 0xCC 0x23 Bit 0: GO0 - - 0xCC Bit 0: GO0 - -

0x41 0x54 0x2B 0x2B 0x2B 0x0D 0xCC 0x43 0x4F 0x4D

0xCC 0x41 0x54 0x4F 0x0D - 0xCC 0x44 0x41 0x54

0x00: Server

Version

- - 0xCC Firmware

0x03: Client

0xCC 0x06 - - - - 0xCC Channel - -

- 0xCC 0x00 or

0x01: Addressed

0xCC 0x10 Byte 4 of dest. MAC Byte 5 Byte 6 0xCC Byte 4 of

0xCC 0x11 - - - - 0xCC Byte 4 of

0xCC Bit 0: Auto Destination

Bit 4: Enable Auto Destination

- - 0xCC MSB of 10

0x02: Temp

Version

0x01

Dest. MAC

Dest. MAC

Bits 1-7: 0

Bit 1: GI1

bit ADC

0x01: Client in Range

0x03: Client out of range

0x00: Server

0x03: Client

- -

Byte 5 Byte 6

Byte 5 Byte 6

- -

LSB of 10 bit ADC

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AC4868 868 MHz Transceiver

Command Name

Command (All bytes in Hex)

Return (All bytes in hex)

User’s Manual

Bit 1: GO1 Bit 1: GO1

Write DAC 0xCC 0x24 Update

Period

Set Max Power 0xCC 0x25 New Max Power - 0xCC Max Power - -

Transmit Buffer Empty 0xCC 0x30 - - - - 0xCC 0x00 - -

Deep Sleep Mode 0xCC 0x86 - - - - 0xCC Channel - -

Read Temperature 0xCC 0xA4 - - - - 0xCC Temp ( C ) - -

EEPROM Byte Read 0xCC 0xC0 Start Address 0xCC Starting

EEPROM Byte Write 0xCC 0xC1 Start Address Length Data Starting Address Length Data

Soft Reset 0xCC 0xFF - - - - - - - -

Duty
Cycle

- - 0xCC Update
Period

Address

Duty Cycle -

Length Data

Command Descriptions

Enter AT Command Mode

Prior to sending this command, the OEM Host must ensure that the transceiver’s RF transmit buffer is empty. If
the buffer is not empty, the radio will interpret the command as data and it will be sent over the RF. This can
be accomplished by waiting up to one second between the last packet and the AT command. RF packet size
must be set to minimum of 6 in order to send this command.

Command: 0x41 0x54 0x2B 0x2B 0x2B 0x0D

Bytes Returned: 4

Response: 0xCC 0x43 0x4F 0x4D

Exit AT Command Mode

The OEM Host should send this command to exit AT Command mode and resume normal operation.

Command: 0xCC 0x41 0x54 0x4F 0x0D

Bytes Returned: 4

Response: 0xCC 0x44 0x41 0x54

Status Request

The OEM Host issues this command to request the status of the transceiver.

Command: 0xCC 0x00 0x00

Bytes Returned: 3

Response: 0xCC Version Data1

Parameters: Data1 = 0x00 for Server

0x01 for Client in Range
0x03 for Client out of Range

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AC4868 868 MHz Transceiver

User’s Manual

Change Server / Client

The OEM Host issues this command to change the transceiver mode from Server to Client and vice versa.

Command: 0xCC 0x03 Data1

Bytes Returned: 3

Response: 0xCC Firmware Version Data1

Parameters: Data1 = 0x00 for Server

0x03 for Client

Sleep Walk Power-Down

After the Host issues this command, the transceiver will de-assert its In_Range line after entering power down.
A Client in power down will remain in sync with a Server for a minimum of 2 minutes. To maintain
synchronization with the Server, the Client should re-sync at least once every 2 minutes. This is done by
sending the Power Down wake up command and waiting for the In_Range line to go active. Once this occurs,
the Client is in sync with the server and can be put back into power-down mode.

Note: This command is valid only for Client transceivers.

Command: 0xCC 0x06

Bytes Returned: 2

Response: 0xCC Channel

Sleep Walk Power-Down Wake Up

The OEM Host issues this command to bring the transceiver out of Power Down mode.

Command: 0xCC 0x07

Bytes Returned: 2

Response: 0xCC Channel

Broadcast Packets

The OEM Host issues this command to change the transceiver operation between Addressed Packets and
Broadcast Packets. If Addressed Packets are selected, the transceiver will send all packets to the transceiver
designated by the Destination Address programmed in the transceiver. If Broadcast Packets are selected, the
transceiver will send its packets to all transceivers on that network. Setting bit-7 of API Control to 1 can also
enable Broadcast Packets.

Command: 0xCC 0x08 Data1

Bytes Returned: 2

Response: 0xCC Data1

Parameters: Data1 = 0x00 for Addressed

0x01 for Broadcast

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AC4868 868 MHz Transceiver

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Write Destination Address

The OEM Host issues this command to the transceiver to change the Destination Address.

Note: Only the three Least Significant Bytes of the MAC Address are used for packet delivery.

Command: 0xCC 0x10 MAC3 MAC2 MAC1

Bytes Returned: 4

Response: 0xCC MAC3 MAC2 MAC1

Parameters: 0x00 – 0xFF, corresponding to 3 LSBs of destination MAC Address

Read Destination Address

The OEM Host issues this command to the transceiver to read the destination address.

Note: Only the three Least Significant Bytes of the MAC Address are used for packet delivery.

Command: 0xCC 0x11

Bytes Returned: 4

Response: 0xCC MAC3 MAC2 MAC1

Parameters: 0x00 – 0xFF, corresponding to 3 LSBs of destination MAC Address

Auto Destination

The Host issues this command to change the Auto Destination setting. When issuing this command, the Auto
Destination setting will only be changed if the corresponding enable bit is set (Control1 Parameter, EEPROM
address 0x56, bits-4,5)

Command: 0xCC 0x15 Data1

Bytes Returned: 2

Response: 0xCC Data2

Parameters: Data 1: bit-0 = Auto Destination,

bit-4 = Enable Auto Destination modification

Data2: bit-0 = New Auto Destination setting

bits 1 – 7 = 0

Read Digital Inputs

The OEM Host issues this command to read the state of both digital input lines.

Command: 0xCC 0x20

Bytes Returned: 2

Response: 0xCC Data1

Parameters: Data1 = bit-0: GI0

bit-1: GI1

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AC4868 868 MHz Transceiver

User’s Manual

Read ADC

The OEM Host issues this command to read any of the three onboard 10-bit A/D converters. Because the RF is
still active in On-the-Fly Command Mode, the transceiver will not process the command until there is no
activity on the network.

Analog Voltage = (10 bits / 0x3FF) * 3.3V

Temperature (˚C) = ((Analog Voltage - 0.3) / 0.01) - 30

Command: 0xCC 0x21 Data1

Bytes Returned: 3

Response: 0xCC Data2 Data3

Parameters: Data1 = 0x00: AD In

0x01: Temperature
Data2 = MSB of requested 10-bit ADC value
Data3 = LSB of requested 10-bit ADC value

Write Digital Outputs

The OEM Host issues this command to write both digital output lines to particular states.

Note: This command should only be used when Protocol Status (0xC2) is not set to 0xE3.

Command: 0xCC 0x23 Data1

Bytes Returned: 2

Response: 0xCC Data1

Parameters: Data1 = bit-0: GO0

bit-1: GO1

Write DAC

The OEM Host issues this command to write DA_Out to a particular voltage. The transceiver uses a PWM
(Pulse Width Modulator) to generate the analog voltage. The theory behind a PWM is that a binary pulse is
generated with a fixed duty cycle and rate. As such, this pin toggles between High & Low. This signal is filtered
via an on-board R-C circuit and an analog voltage is generated. Duty cycle specifies the ratio of time in one
cycle that the pulse spends High proportionate to the amount of time it spends Low. So, with a duty cycle of
50% (0x80), the pulse is High 50% of the time and Low 50% of the time; therefore the analog voltage would
be half of 3.3V or 1.15V. A broad filter has been implemented on the transceiver and there is no advantage to
using a slower update period. Generally, a faster update period is preferred.

Command: 0xCC 0x24 Data1 Data2

Bytes Returned: 3

Response: 0xCC Data1 Data2

Parameters: Data1 = Update period

Data2 = Duty cycle

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( × ())

=

.







=





× 3.3

AC4868 868 MHz Transceiver

User’s Manual

Set Max Power

The OEM Host issues this command to limit the maximum transmit power emitted by the transceiver. This can
be useful to minimize current consumption and satisfy certain regulatory requirements. The radios are shipped
at maximum allowable power.

Command: 0xCC 0x25 Max Power

Bytes Returned: 2

Response: 0xCC Max Power

Transmit Buffer Empty

The OEM Host issues this command to determine when the RF transmit buffer is empty. The Host will not
receive the transceiver response until that time.

Command: 0xCC 0x30

Bytes Returned: 2

Response: 0xCC 0x00

Deep Sleep Mode

The OEM Host issues this command to put the transceiver into Deep Sleep mode. Once in Deep Sleep mode,
the transceiver disables all RF communications and will not respond to any further commands until being reset
or power-cycled. This command is valid for both Servers and Clients.

Command: 0xCC 0x86

Bytes Returned: 2

Response: 0xCC Channel

Read Temperature

The OEM Host issues this command to read the onboard temperature sensor. The transceiver reports the
temperature in ˚C where 0x00 - 0x50 maps to 0 - 80 ˚C and where 0xD8 - 0x00 maps to -40 - 0 ˚C.

EEPROM Byte Read

Upon receiving this command, a transceiver will respond with the desired data from the addresses requested
by the OEM Host.

Command: 0xCC 0xC0 Data1 Data2

Bytes Returned: 4+

Response: 0xCC Data1 Data2 Data3

Parameters: Data1 = EEPROM Address

Data2 = Length (0x00 – 0x80)
Data3 = Requested data

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AC4868 868 MHz Transceiver

User’s Manual

EEPROM Byte Write

Upon receiving this command, a transceiver will write the data byte to the specified address but will not echo
it back to the OEM Host until the EEPROM write cycle is complete (up to 10 ms).

Multiple byte writes of up to 128 bytes are allowed. An EEPROM boundary exists between addresses 0x7F and
0x80. No single EEPROM write command shall write to addresses on both sides of that EEPROM boundary.

Command: 0xCC 0xC0 Data1 Data2

Bytes Returned: 4+

Response: 0xCC Data1 Data2 Data

Parameters: Data1 = EEPROM Address

Data2 = Length (0x00 – 0x80)
Data3 = Last byte of data written

Reset

The OEM Host issues this command to perform a soft reset of the transceiver. Any transceiver settings
modified by CC commands will revert to the values stored in the EEPROM.

Command: 0xCC 0xFF

Bytes Returned: None

Response: None

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AC4868 868 MHz Transceiver

Parameter

EEPROM
Address

Length
(bytes)

Range

Default

Description

User’s Manual

EEPROM PARAMETERS

The OEM Host can program various parameters that are stored in EEPROM which become active after a
power-on reset. The table below gives the locations and descriptions of the parameters that can be
read/written by the OEM Host. Factory default values are also shown. Do not write to any EEPROM addresses
other than those listed below. Do not copy one transceiver’s EEPROM to another transceiver as doing so may
cause the transceiver to malfunction.

Table 11: EEPROM Parameters

Product ID 0x00 40 40 bytes - Product identifier string. Includes

revision information for software and hardware.

Beacon Period 0x3C 2 0x01 –

0xFF

Range Refresh 0x3D 1 0x01 –

0xFF

Stop Bit Delay 0x3F 1 0x01 –

0xFF

Channel
Number

Server/Client
Mode

Baud Rate Low 0x42 1 0x00 –

Baud Rate High 0x43 1 0x00 0x00 High byte of interface baud. Always 0x00

Control 0 0x45 1 0x00 –

0x40 1 0x38 0x38

0x41 1 0x01 –

0x02

0xFF

0xFF

0x14 Specifies the number of hop periods between

Server beacon transmissions (equal to 53ms *
value). Note that each transceiver should only
transmit 10% of the time and beacons count as
transmissions.

0x18 Specifies the maximum amount of time a

transceiver will report In Range without having
heard a Server’s beacon (equal to hop period *
value). Do not set to 0x00.

0xFF For systems employing the RS-485 interface or

Parity, the serial stop bit might come too early.
Stop bit delay controls the width of the last bit
before the stop bit occurs.

0xFF = Disable Stop Bit Delay (12 us)
0x00 = (256 * 1.6 us) + 12 us
0x01 - 0xFE = (value * 1.6 us) + 12 us

0x02 0x01 = Server

0x02 = Client

0xFC Low byte of the interface baud rate. Default

baud rate is 57,600.

0x14 Settings are:

bit-7: Laird Technologies Use Only
bit-6: DES Enable
bit-5: Laird Technologies Use Only
bit-4: Laird Technologies Use Only
bit-3: Laird Technologies Use Only
bit-2: Laird Technologies Use Only
bit-1: RF Delivery
0 = Addressed packets
1 = Broadcast packets
bit-0: Laird Technologies Use Only

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AC4868 868 MHz Transceiver

Parameter

EEPROM
Address

Length
(bytes)

Range

Default

Description

Note

User’s Manual

Transmit Retries 0x4C 1 0x01 –

0xFF

Broadcast
Attempts

0x4D 1 0x01 –

0xFF

API Control 0x56 1 0x00 –

0xFF

Interface
Timeout

0x58 1 0x02 –

0xFF

RF Packet Size 0x5B 1 0x01 –

0xFF

CTS On 0x5C 1 0x01 –

0xFF

CTS Off 0x5D 1 0x00 –

0xFE

Max Power 0x63 1 0x00 –

0x60

Parity 0x6F 1 0xE3,

0xFF

0x10 Maximum number of times a packet is sent out

when Addressed packets are selected.

0x04 Maximum number of times a packet is sent out

when Broadcast packets are selected.

0x43 Settings are:

bit-7: Laird Technologies Use Only
bit-6: Laird Technologies Use Only
bit-5: Unicast Only
0 = Disabled
1 = Enabled
bit-4: Auto Destination
0 = Use destination address
1 = Use auto destination
bit-3: Laird Technologies Use Only
bit-2: RTS Enable
0 = Ignore RTS
1 = Transceiver obeys RTS
bit-1: Duplex
0 = Half Duplex
1 = Full Duplex
bit-0: Auto Config
0 = Use EEPROM values
1 = Auto Configure values

0x04 Specifies a byte gap timeout, used in

conjunction with RF Packet Size to determine
when a packet coming over the interface is
complete (0.5 ms per increment).

0x24 Used in conjunction with Interface Timeout;

specifies the maximum size of an RF packet.
When Auto Config is enabled, this value is
overridden based on the Interface Baud Rate
and RF Delivery mode. Must be set to a
minimum of 6 in order to send the Enter AT
command.

0xC0 CTS will be deasserted (High) when the transmit

buffer contains at least this many characters.

0xB0 Once CTS has been deasserted, CTS will be

reasserted (Low) when the transmit buffer is
contains this many or less characters.

Set at
produc.,
varies

Used to increase/decrease the output power.
The transceivers are shipped at maximum
allowable power.

0xFF 0xE3 = Enable Parity

0xFF = Disable Parity

: Enabling parity cuts throughput and the

interface buffer size in half.

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AC4868 868 MHz Transceiver

Parameter

EEPROM
Address

Length
(bytes)

Range

Default

Description

User’s Manual

Destination ID 0x70 6 0x00 –

0xFF Specifies destination for RF packets

0xFF

System ID 0x76 1 0xE3,

0xFF

0xFF Similar to network password. Radios must have

the same system ID to communicate with each
other.

RS-485 DE 0x7F 1 0xE3,

0xFF

0xFF 0xE3 = GO0 is active Low DE for control of

external RS-485 hardware
0xFF = Disable RS-485 DE

MAC ID 0x80 6 0x00 –

Factory programmed unique IEEE MAC address.

0xFF

Original Max
Power

0x8E 1 Set in

prod. ,
varies

Copy of original max power EEPROM setting.
This address may be referenced but should not
be modified.

Product ID 0x90 15 0x90 - 0x93: Product ID

0x94 - 0x95: Prefix (AC)
0x96 - 0x99: Power (250M)
0x9A - 0x9C: Interface (485, TTL)
0x9D - 0x9E: Setup script (01 is stock)
0x9F: Reserved for future use; always 0xFF

DES Key 0xD0 7 0x00 –

56-bit Data Encryption key

0xFF

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AC4868 868 MHz Transceiver

User’s Manual

DIMENSIONS

Mechanical Drawings

Interface Connector - 20 pin OEM Interface connector (Molex 87759-0030, mates with Samtec
SMM-110-02-S-D

MMCX Jack - Antenna Connector (Johnson Components 135-3711-822)

Figure 9: AC4868-250 (with MMCX connector) Mechanical

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AC4868 868 MHz Transceiver

User’s Manual

ORDERING INFORMATION

Product Part Number Tree

Developer Kit Part Numbers

All of the above part numbers can be ordered as a development kit by prefacing the part number with
“SDK-”. As an example, part number AC4868-250M can be ordered as a development kit using the part
number: SDK-AC4868- 250M.

All developer’s kits include (2) transceivers, (2) development boards, (2) 7.5 VDC unregulated power supplies,
(2) serial cables, (2) USB cables, (2) antennas, configuration/testing software and integration engineering
support.

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AC4868 868 MHz Transceiver

Part Number

EUR/EN

Laird Part #

Manufacturer Part #

Manufacturer

Type

Gain
(dBi)

200A

200M

1000M

User’s Manual

COMPLIANCY INFORMATION

Agency Identification Numbers

Agency compliancy is a very important requirement for any product development. Laird Technologies has
obtained modular approval for its products so the OEM only has to meet a few requirements to be eligible to
use that approval. The corresponding agency identification numbers and approved antennas are listed below.

Table 12: Agency Identification Numbers

AC4868-250M Approved

Approved Antenna List

The following antennas are approved for use with the AC4868-250 as identified. The OEM is free to choose
another vendor’s antenna of like type and equal or lesser gain as a listed antenna and still maintain
compliance.

Table 13: AC4868-250 Approved Antennas

0600-00020 S467-FL-6-RMM-868S Nearson ½ Wave Dipole 2 - X X

OEM Equipment Labeling Requirements

WARNING: The OEM must ensure that the appropriate labeling requirements are met. Following are the
requirements for labeling equipment:

 If the CE marking is reduced or enlarged, the proportions given in the following graduated drawing must

be respected.

 The CE marking must have a height of at least 5 mm except where this is not possible on account of the

nature of the apparatus.

 The CE marking must be affixed to the product or to its data plate. Additionally, it must be affixed to the

packaging, if any, and to the accompanying documents.

 The CE marking must be affixed visibly, legibly, and indelibly.
 The exclamation point must be included with the CE mark (as shown below) to alert the user that there

are restrictions placed on usage in certain countries. It must have the same height as the CE mark.

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AC4868 868 MHz Transceiver

RF Channel

Country

Restriction

Reason / Remarks

User’s Manual

Country Restrictions

The exclamation point included with the CE mark denotes that the equipment has restrictions in certain
countries. Following is a list of countries having restrictions on the AC4868 and a description of those
restrictions. The OEM is responsible for ensuring that these restrictions are met.

0x38 Al countries (unless

otherwise noted)

0x38 Bulgaria Not implemented

0x38 Finland Audio and voice are not permitted

0x38 Germany Audio and voice are not permitted

0x38 Italy Maximum EIRP of 25mW Military applications

0x38 Slovak Republic Not implemented Military

Maximum ERP of 500 mW and max transmit
duty cycle of 10% (amortized over one hour)

Country Notification

The OEM is responsible for notifying ANY country of the intent to ship product to that country containing the
AC4868 four weeks prior to shipping.

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AC4868 868 MHz Transceiver

User’s Manual

Declaration of Conformity

Laird Technologies has issued a Declaration of Conformity for the AC4868-250M transceiver module
concerning emissions, EMC, and safety. The Declaration of Conformity is a document that lists the product
name and band of use and must appear in the OEM user’s manual.

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AC4868 868 MHz Transceiver

Qty

Reference

Value

Description

Mfg.

Mfg. Part #

User’s Manual

APPENDIX I: SAMPLE POWER SUPPLY

Below is a simple switching power supply that provides enough current to easily power any Laird Technologies
OEM module. It utilizes low cost, off the shelf components that fit into a small area. This supply has an input
voltage range of +6 volts to +18 volts and will output +3.4 volts at 1.5 amps.

Included is a schematic, bill of materials with manufacture's name and part numbers and a sample PCB layout.
It is important to follow the layout suggestions and use large areas of copper to connect the devices as shown
in the layout. It is also important to hook up the ground traces as shown and use multiple vias to connect
input and output capacitors to the bottom side ground plane.

If the input voltage will be less than 12 volts then C1 and C2 can be replaced with a single 100uF 20 volt
capacitor (same part number as C7). This will reduce board space and lower costs further. If you are powering
an AC5124 module, R1 can be changed to a 373 ohm 1% resistor. This will change the output to +5 volts at

1.0 amps.

Bill of Materials

1 R1 210 Res, 0603, 210, 1/16W, 1% KOA RK73H1JT2100F

1 R2 127 Res, 0603, 127, 1/16W, 1% KOA RK73H1JT1270F

2 C1 C2 47uF Cap, Tant, 7343, 47uF, 35V AVX TPSE476M035R0200

3 C3 C4 C5 0.1uF Cap, Cer, 0603, 0.1uF, Y5V,

25V

1 C6 3300pF Cap, Cer, 0603, 3300pF, X7R,

50V

1 C7 100uF Cap, Tant, 7343, 100uF, 20V Kemet T491X107K020A5

1 D1 B230/A Diode, SMB, B230/A, 2A,

Schottkey

1 D2 LL4148 Diode, MELF, LL4148, Switch

Diode

1 L1 15uH Xfmr, 2P, SMT, 15uH, 2A Coiltronics UP2.8B150

1 U1 CS51413 IC, CS51413, 8P, SO, Switch

Reg Ctrl.

Murata GRM39Y5V104Z025AD

Murata GRM39X7R332K050AD

Diodes, Inc. B230/A

Diodes, Inc. LL4148

On-Semicond. CS51413

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AC4868 868 MHz Transceiver

User’s Manual

Schematic

PCB Layout

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AC4868 868 MHz Transceiver

User’s Manual

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AC4868 868 MHz Transceiver

User’s Manual

APPENDIX II: 5V TO 3.3V LEVELS

All inputs on the AC4868-250 are weakly pulled high via 10 kohm resistors. The AC4868-250 has 3.3V only
inputs. Some of the most common voltage conversion methods are described below.

Voltage Level Conversion ICs

This is the easiest and most efficient method. Laird Technologies recommends the TI SN74LVC244A Octal
Buffer/Driver. Inputs can be driven from either 3.3 or 5V systems, allowing the device to be used in a mixed

3.3/5V system.

Passive Resistor Voltage Divider

While a resistor voltage divider can successfully drop the 5V to the required 3.3V, it will draw static current all
of the time. Typically this method is only suitable for one-way 5V to 3.3V conversion. When choosing the
resistor values, one needs to include the radio’s internal 10 kohm resistors on the input signals.

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