sylvac PLC Mode D'emploi page 59

Normal response frame format
Function code (8 bits)
Exception response frame format
Function code + 0x80 (8 bits)
Table of supported modbus functions
Function code
01
02
03
04
05
06
07
08 00
08 01
Data (any bits)
Exception code (8 bits)
Description
Read n bits
Read n registers
Write 1 bit
Write 1 register
Read fast status byte
Echo diagnostic
Restart communication (vvvv =
0xFF00 to clear the event counter
of function 11, 0x0000 to keep it)
Error check (CRC) (16 bits)
Error check (CRC) (16 bits)
PDU request format
0x01 aaaa nnnn
0x02 aaaa nnnn
0x03 aaaa nnnn
0x04 aaaa nnnn
0x05 aaaa yy00
0x06 aaaa vvvv
0x07
0x08 0x00 llll
0x08 0x01 vvvv
PDU answer format
0x01 bb ll
0x02 bb ll
0x03 bb ll
0x04 bb ll
0x05 aaaa yy00
0x06 aaaa vvvv
0x07 ff
The bit 0 set in ff indicates a new
available position
0x08 0x00 llll
0x08 0x01 vvvv