7> Modbus Rs-485 Communication Function - S&A CWFL-6000 User Manual

<7> MODBUS RS-485 communication
function
This system adapts salve mode of MODBUS-RTU communication,9600 baud rate,
no parity checking,8 data bit,1 stop bit and support MODBUS-RTU 03 (Read
Holding Registers) and 06 (Read Holding Registers) commands. Communication
formats are as below:
1. Command format 03
Host send command
Function code 1 bytes
Initial address 2 bytes
Register number 2 bytes
Slave response
Function code 1 bytes
Number of bytes 1 bytes
Register value N*2 bytes
Error
Error code 1 bytes
Exception code 1 bytes
For example: if the host's sending address is 1, requests 108-110 command of
slave read register and send 01 03 00 6B 00 03 XX YY,thereinto,01 as slave
address, 03 as function code, 00 6B as initial address, 00 03 as register number
and XX YY as the result of CRC verification.
Slave response: 01 03 06 02 2B 00 00 00 64 XX YY, thereinto, 01 as slave address,
03 as function code, 06 as number of bytes, 02 2B 00 00 00 64 corresponding to
the values in 108-110 of register respectively and XX YY as verification code.
If the slave receives wrong data, return to data 01 83 01 XX YY, thereinto, 01 as
slave address. 83 as error code, 01 as exception code and XX YY as check sum.
2. Command format 06
Host send command
Function code 1 bytes
Register address 2 bytes
Register value 2 bytes
0x03
From 0x0400 to 0x044a, From 0x0100 to 0x0108,
From 0x0800 to 0x0803
From 1 to 10
0x03
2*N（ "N" is the number of registers ）
0x83
01 or 02 or 03 or 04
0x06
From 0x0400 to 0x044a
From 0x000 to 0xffff
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CWFL-6000 Series