COMMERCIAL IN CONFIDENCE
Page 12
2.4.3 Force Single Coil (write single bit)
Byte No Meaning Value (hex)
1 Slave address xx
2 ModBus Function code (force coil) 05
3 Starting Address MSB, always 00, all bits are in internal
memory
00
4 Starting Address LSB xx
5 Force Data MSB (FF sets the bit, 00 clears it) FF or 00
6 Force Data LSB (always 00) 00
7 CRC lo byte ??
8 CRC hi byte ??
An error response code 2 (illegal address) will be returned if the bit is not a valid writeable bit,
otherwise the response is the same as the above message.
2.4.4 Preset Single Register
Byte No Meaning Value (hex)
1 Slave address xx
2 ModBus Function code (write register) 06
3 Starting Address MSB xx
4 Starting Address LSB xx
5 Data MSB xx
6 Data LSB xx
7 CRC lo byte ??
8 CRC hi byte ??
The normal response is the same as the message. An error response code 2 (illegal address)
will be returned if the address is not within the processor bounds.
2.4.5 Preset Multiple Registers
Byte No Meaning Value (hex)
1 Slave address xx
2 ModBus Function code (write register) 10
3 Starting Address MSB xx
4 Starting Address LSB xx
5 Number of registers MSB 00
6 Number of registers LSB 01
7 Number of bytes to follow 02
8 Data MSB xx
9 Data LSB xx
10 CRC lo byte ??
11 CRC hi byte ??
note that this function is a subset of the normal ModBus function code 16 in that only one register of up
to 2 bytes may be written. Thus byte numbers 5, 6 and 7 must be as shown, otherwise an error
response with error code 1 (illegal request) will be returned.
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