Datakom DKM-411, Applications Manual

Page: 9 / 16

DKM-411 Modbus Application Manual V3.0
(15.01.2017)
- 9 -
The function 06 (write single register) and the function 16 (write multiple registers) are used for data
writing.
The MODBUS master will send a query containing data to be written. The answer will be one of the below:
-A normal response confirming successful write,
-An exceptional response indicating a write error.
Only some of the available registers are authorized to be written. An attempt to write a write protected
register will result to the exceptional response.
The query message specifies the register address and data. The message structure is below:
Byte Description Value
0 Controller address 1 to 240
1 Function code 16
2 Starting address high See below the description of available registers
3 Starting address low
4 Number of registers high always 0
5 Number of registers low max ??
6
Data lenght in bytes (L)
number of registers * 2
7 High byte of 1st register
8 Low byte of 1st register
9 High byte of 2nd register
10 Low byte of 2nd register
....
L+5 High byte of the last register
L+6 Low byte of the last register
L+7 CRC low byte See below for the checksum calculation
L+8 CRC high byte
The normal response is below:
Byte Description Value
0 Controller address 1 to 240
1 Function code 16
2 Starting address high See below the description of available registers
3 Starting address low
4 Number of registers high always 0
5 Number of registers low max ??
6 CRC low byte See below for the checksum calculation
7 CRC high byte
The exceptional response will be:
Byte Description Value
0 Controller address same as in the query
1 Function code 144 (function code + 128)
2 Exception code 2 (illegal address)
or
10 (write protection)
3 CRC low byte See below for the checksum calculation
4 CRC high byte
DATA WRITING (MULTIPLE REGISTERS)