Descriptions of functions
10.8 Communication via Modbus TCP
SINAMICS DCM DC Converter
Operating Instructions, 12/2018, A5E34763375A
545
Structure of a write request via Modbus function code 06 (FC 06)
Start address is the holding register address.
Via FC 06, with one request, only precisely one register can be addressed. The value, which
is written to the addressed register, is contained in bytes 10 and 11 of the write request.
Table 10- 53 Structure of a write request for device number 17, example
Value
Byte
Description
MBAP header
06 h
00 h
63 h
55 h
66 h
7
8
9
10
11
Function code
Register start address "High" (write register 40100)
Register start address "Low"
Register data "High"
Register data "Low"
The response returns register address (bytes 8 and 9) and the value (bytes 10 and 11),
which the higher-level control had written to the register.
Table 10- 54 Device response to the write request, example
Value
Byte
Description
MBAP header
06 h
00 h
63 h
55 h
66 h
7
8
9
10
11
Function code
Register start address "High"
Register start address "Low"
Register data "High"
Register data "Low"
Table 10- 55 Invalid write request
Write request
Inverter response
Incorrect address (a holding register address does not exist)
Exception Code 02 - invalid data
address
Write to a "read-only" register
Exception Code 04 - device failure
Write to a reserved register
For Exception Code 4, via the holding register 40499, you can read out the internal drive
error code, which has occurred for the last parameter access via the holding register.
10.8.5
Communication via data set 47
Via FC 16, with one request, up to 122 registers can be written to directly one after the other,
while for Write Single Register (FC 06) you must individually write the header data for each
register.
