156 Fieldbus Communication
WAGO-I/O-SYSTEM 750 XTR
750-352/040-000 FC ETHERNET G3 XTR
Manual
Version 1.3.0
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
hex
... FF
hex
] and an offset of 1000
hex
(0x01000) to the
MODBUS addresses in the range of [6000
hex
... 62FC
hex
].
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
Field name
Example
Byte 0, 1
Transaction identifier
0x0000
Byte 2, 3
Protocol identifier
0x0000
Byte 4, 5
Length field
0x0006
Byte 6
Unit identifier
0x01 not used
Byte 7
MODBUS function code
0x01
Byte 8, 9
Reference number
0x0000
Byte 10, 11
Bit count
0x0008
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
Field name
Example
...
Byte 7
MODBUS function code
0x01
Byte 8
Byte count
0x01
Byte 9
Bit values
0x12
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
