User manual for - TIMER SLC-94
9.2.
TRANSMISSION ERRORS DESCRIPTION
If an error occurs while write or read of single register, then the device sends an error
code according to Modbus RTU specifications (example message no 7).
Error codes:
01h
- illegal function (only functions 03h and 06h are available),
02h
- illegal register address
03h
- illegal data value
08h
- no write permission ( see: “
mbAccE
” parameter)
9.3.
EXAMPLES OF QUERY/ANSWER FRAMES
Examples apply for device with address 1. All values are represent hexadecimal.
Field description:
ADDR
Device address on Modbus network
FUNC
Function code
REG H,L
Starting address (address of first register to read/write, Hi and Lo byte)
COUNT H,L
No. of registers to read/write (Hi and Lo byte)
BYTE C
Data byte count in answer frame
DATA H,L
Data byte (Hi and Lo byte)
CRC L,H
CRC
error check (Hi and Lo byte)
1. Read of ID code
ADDR
FUNC
REG H,L
COUNT H,L
CRC L,H
01
03
00
21
00
01
D4
00
The answer:
ADDR
FUNC
BYTE C
DATA H,L
CRC L,H
01
03
02
00
7B
F8
67
DATA - identification code (007Bh)
2. Change of the device address from 1 to 2 (write to reg. 20h)
ADDR
FUNC
REG H,L
DATA H,L
CRC L,H
01
06
00
20
00
02
09
C1
DATA H - 0
DATA L - new device address (2)
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