Function Code Fc1 (Read Coils); Table 71: Request Of Function Code Fc1; Table 72: Response Of Function Code Fc1 - WAGO -I/O-SYSTEM 750 XTR Manual

156 Fieldbus Communication
Reading and writing of outputs via FC1 to FC4 is also possible by adding
an offset!
In the case of the read functions (FC1 ... FC4) the outputs can be additionally
written and read back by adding an offset of 200hex (0x0200) to the MODBUS
addresses in the range of [0
MODBUS addresses in the range of [6000
11.2.3.1

Function Code FC1 (Read Coils)

This function reads the status of the input and output bits (coils) in a slave device.
Request
The request specifies the reference number (starting address) and the bit count
to read.
Example: Read output bits 0 to 7.

Table 71: Request of Function Code FC1

Byte
Byte 0, 1
Byte 2, 3
Byte 4, 5
Byte 6
Byte 7
Byte 8, 9
Byte 10, 11
Response
The current values of the response bits are packed in the data field. A binary 1
corresponds to the ON status and a 0 to the OFF status. The lowest value bit of
the first data byte contains the first bit of the request. The others follow in
ascending order. If the number of inputs is not a multiple of 8, the remaining bits
of the last data byte are filled with zeroes (truncated).

Table 72: Response of Function Code FC1

Byte
...
Byte 7
Byte 8
Byte 9
The status of the inputs 7 to 0 is shown as byte value 0x12 or binary 0001 0010.
Input 7 is the bit having the highest significance of this byte and input 0 the
Manual
Version 1.3.0
750-352/040-000 FC ETHERNET G3 XTR
... FF ] and an offset of 1000
hex hex
... 62FC
hex
Field name
Transaction identifier
Protocol identifier
Length field
Unit identifier
MODBUS function code
Reference number
Bit count
Field name
MODBUS function code
Byte count
Bit values
WAGO-I/O-SYSTEM 750 XTR
(0x01000) to the
hex
].
hex
Example
0x0000
0x0000
0x0006
0x01 not used
0x01
0x0000
0x0008
Example
0x01
0x01
0x12