Siemens SITRANS F Modbus RTU RS 485 Operating Instructions Manual page 25

The data section of the response message contains a number of bits representing the status of
the coils(s) that has been read from the device. The LSB of the coil status byte indicates the status
of the coil.
Table 6-3
Message byte
Slave address
Function code
Bit count
Coil status byte(s)
Next coil status byte(s)
Last coil status byte(s)
CRC-16
Exception response
The exception response message contains the same slave address as the command message.
The function code of the exception message is actually a value of 80 hex plus the original
function code of 01 hex .
The exception code indicates where the error occurred in the command message. A complete
listing of exception codes is shown in a later chapter.
Table 6-4
Message byte
Slave address
Function code
Exception code
CRC-16
Example
Read Coil Totalizer 1 (0:00011):
• Query: 1,1,0,10,0,1,221,200 (Hex 01,01,00,10,00,01,DD,C8)
• Response: 1,1,1,0,81,136 (Hex 01,01,01,00,51,88)
Modbus RTU RS 485
Operating Instructions, 03/2021, A5E00753974-AB
Read coil normal response messages
Lower
Upper
Read coil exception response messages
Lower
Upper
Functions codes
6.2 Read coils
Example
xxhex
01hex
xxhex
xxhex
xxhex
xxhex
xxhex
xxhex
xxhex
xxhex
xxhex
Example
xxhex
81hex
02hex
xxhex
xxhex
25