IM-P405-39 AB Issue 1
47
Format: Byte
Start 1 bit
Data 8 bit
Parity 0 bit
Stop 1 bit
Format: Request frame
Address 1 byte
Function code 1 byte
Start address 2 bytes
Quantity of registers 2 bytes
Cyclic redundancy check (CRC) 2 bytes
Total 8 bytes
Format: Response frame
Address 1 byte
Function code 1 byte (or error code, see below)
Byte count 1 byte (or exception code, see below)
Register data 2 bytes, most significant first
Error check (CRC) 2 bytes
Total 7 bytes if correct (or 5 bytes if in error)
Only Function Code 03, 'Read holding registers' is allowed.
Parameters and register data
Register Parameters
0 6 - Identity
1 Timer 1 data (day)
2 Timer 1 start (time)
3 Timer 1 duration (seconds)
4 Timer 2 data (day)
5 Timer 2 start (time)
6 Timer 2 duration (seconds)
7 Timer 3 data (day)
8 Timer 3 start (time)
9 Timer 3 duration (seconds)
The format of the register data is 16 bit integer, with the most significant byte transmitted
first.
Exception codes
01 illegal function
02 illegal data address
11. Appendix -
Summary of the Modbus protocol
