Function Code Fc15 (Force Multiple Coils) - WAGO 750 Series Manual

170 • MODBUS Functions
Description of the MODBUS Functions

6.3.8 Function Code FC15 (Force Multiple Coils)

This function sets a sequence of output bits to 1 or 0 in a slave device. The
maximum number is 256 bits.
Request
The request message specifies the reference number (first coil in the
sequence), the bit count (number of bits to be written), and the output data.
The output coils are zero-based; therefore, the first output point is 0.
In this example 16 bits are set, starting with the address 0. The request
contains 2 bytes with the value 0xA5F0, or 1010 0101 1111 0000 in binary
format.
The first data byte transmits the value of 0xA5 to the addresses 7 to 0,
whereby 0 is the lowest value bit. The next byte transmits 0xF0 to the
addresses 15 to 8, whereby the lowest value bit is 8.
Byte
Byte 0, 1
Byte 2, 3
Byte 4, 5
Byte 6
Byte 7
Byte 8, 9
Byte 10, 11
Byte 12
Byte 13
Byte 14
Response
Byte
.....
Byte 7
Byte 8, 9
Byte 10, 11 Bit Count
Exception
Byte
.....
Byte 7
Byte 8
Field name
Transaction identifier
protocol identifier
Length field
unit identifier
MODBUS function code
reference number
Bit Count
Byte Count
Data Byte1
Data Byte2
Field name
MODBUS function code
Reference number
Field name
MODBUS function code
Exception code
Example
0x0000
0x0000
0x0009
0x01 not used
0x0F
0x0000
0x0010
0x02
0xA5
0xF0
Example
0x0F
0x0000
0x0010
Example
0x8F
0x01 or 0x02
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