Beijer Electronics AN-BEI-H2-038 - Manual (Page 2)

APPLICATION NOTE AN‐BEI‐H2‐038 Date: 15/02/12
AN‐BEI‐H2‐038 Modbus RTU Control and Register Mapping 2
Modbus Telegram Structure:
The following Modbus Commands are supported
• 03 Read Holding Registers
• 06 Write Single Holding Register
The telegram structure is as follows:‐
Command 03 – Read Holding Registers Command 06 – Write Single Holding Register
Master Telegram Length Slave Response Length Master Telegram Length Slave Response Length
Slave Address 1 Byte Slave Address 1 Byte Slave Address 1 Byte Slave Address 1 Byte
Function Code (03) 1 Byte Function Code (03) 1 Byte Function Code (06) 1 Byte Function Code (06) 1 Byte
1st Register Address 2 Bytes Byte Count 1 Byte Register Address 2 Bytes Register Address 2 Bytes
No. Of Registers 2 Bytes 1st Register Value 2 Bytes Value 2 Bytes Register Value 2 Bytes
CRC Checksum 2 Bytes 2nd Register Value 2 Bytes CRC Checksum 2 Bytes CRC Checksum 2 Bytes
Etc...
CRC Checksum 2 Bytes
RJ45 Data Connection Pin Configuration:
CAN‐
CAN+
0 Volt
Optibus / Remote Keypad / PC Connection ‐
Optibus / Remote Keypad / PC Connection +
+24 Volt Remote Keypad Power Supply
RS 485‐ Modbus RTU
RS 485+ Modbus RTU
Typical MODBUS configuration: