Technical data

Fieldbus Communication • 225
MODBUS Functions
WAGO-I/O-SYSTEM 750
BACnet/IP Controller
4.3.3.8 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 se-
quence), 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 con-
tains 2 bytes with the value 0xA5F0, or 1010 0101 1111 0000 in binary for-
mat.
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 ad-
dresses 15 to 8, whereby the lowest value bit is 8.
Byte Field name Example
Byte 0, 1 Transaction identifier 0x0000
Byte 2, 3 protocol identifier 0x0000
Byte 4, 5 Length field 0x0009
Byte 6 unit identifier 0x01 not used
Byte 7 MODBUS function code 0x0F
Byte 8, 9 reference number 0x0000
Byte 10, 11 Bit Count 0x0010
Byte 12 Byte Count 0x02
Byte 13 Data Byte1 0xA5
Byte 14 Data Byte2 0xF0
Response
Byte Field name Example
.....
Byte 7 MODBUS function code 0x0F
Byte 8, 9 Reference number 0x0000
Byte 10, 11 Bit Count 0x0010
Exception
Byte Field name Example
.....
Byte 7 MODBUS function code 0x8F
Byte 8 Exception code 0x01 or 0x02