Carbon Monoxide Transmitter Modbus
Installation Manual
May 5, 2017
IN-CMD5B4MOD-01-01 Page 22
Exception response
Slave address
(0x01 to 0xFF)
Function
code + 0x80
Exception code *
0x01, 0x02 or 0x03
CRC
LSB
CRC
MSB
* An exception response is only returned if the CRC is correct
Exception code 01 --- illegal function, 02 --- illegal address, 03 --- illegal data value
Function codes (ASCII mode)
0x03 --- Read holding registers
Query
Start
character
(:) 0x3A
Slave address
0x01 to 0xFF
MSB
Slave address
0x01 to 0xFF
LSB
Function
code (0x03)
MSB (0x30)
Function
code (0x03)
LSB (0x33)
Starting
address
MSB
Starting
address
Starting
address
Starting
address
LSB
Quantity of
registers MSB
Quantity
of registers
Quantity
of registers
Quantity of
registers LSB
LRC
MSB
LRC
LSB
Return-line feed
(CRLF) 0x0D
Return-line feed
(CRLF) 0x0A
* Starting address = 0x0000 to 0xFFFF, Quantity of registers = 0x0000 to 0x007D
Response
Start
character (:)
0x3A
Slave address
0x01 to 0xFF
MSB
Slave address
0x01 to 0xFF
LSB
Function
code (0x03)
MSB (0x30)
Function
code (0x03)
LSB (0x33)
Byte
count
MSB (N)
Byte
count
LSB (N)
Register value
MSB
Register
value
Register
value
Register value
LSB
LRC
MSB
LRC
LSB
Return-line feed
(CRLF) 0x0D
Return-line feed
(CRLF) 0x0A
* N= Quantity of registers
0x06 --- Write single register
Query
Start
character
(:) 0x3A
Slave address
0x01 to 0xFF
MSB
Slave address
0x01 to 0xFF
LSB
Function
Code (0x06)
MSB (0x30)
Function
Code (0x06)
LSB (0x36)
Register
address
MSB
Register
address
Register
address
Register
address
LSB
Register
value MSB
Register
value
Register
value
Register
value LSB
LRC
MSB
LRC
LSB
Return-line feed
(CRLF) 0x0D
Return-line feed
(CRLF) 0x0A
* Register address = 0x0000 to 0xFFFF, Registers value = 0x0000 to 0xFFFF
Response
Start
character
(:) 0x3A
Slave address
0x01 to 0xFF
MSB
Slave address
0x01 to 0xFF
LSB
Function
Code (0x06)
MSB (0x30)
Function
Code (0x06)
LSB (0x36)
Register
address
MSB
Register
address
Register
address
Register
address
LSB
Register
value MSB
Register
value
Register
value
Register
value LSB
LRC
MSB
LRC
LSB
Return-line feed
(CRLF) 0x0D
Return-line feed
(CRLF) 0x0A