WAGO 750-830 Manual page 218

218 • Fieldbus Communication
MODBUS Functions
4.3.3.1 Function Code FC1 (Read Coils)
This function reads the status of the input and output bits (coils) in a slave de-
vice.
Request
The request specifies the reference number (starting address) and the bit count
to read.
Example: Read output bits 0 to 7.
Byte
Byte 0, 1
Byte 2, 3
Byte 4, 5
Byte 6
Byte 7
Byte 8, 9
Byte 10, 11 Bit count
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 as-
cending 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).
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 lowest value. The assignment is thus made from 7 to 0 with OFF-OFF-
OFF-ON-OFF-OFF-ON-OFF.
Bit:
Coil:
Exception
Byte
.....
Byte 7
Byte 8
Field name
Transaction identifier
protocol identifier
length field
unit identifier
MODBUS function code
reference number
Field name
MODBUS function code
Byte count
Bit values
0 0 0 1 0 0 1 0
7 6 5 4 3 2 1 0
Field name
MODBUS function code
Exception code
Example
0x0000
0x0000
0x0006
0x01 not used
0x01
0x0000
0x0008
Example
0x01
0x01
0x12
Example
0x81
0x01 or 0x02
WAGO-I/O-SYSTEM 750
BACnet/IP Controller