Communication Procedure - Siemens Sinamics G120P Operating Instructions Manual

If an incorrect address is entered (a holding register address does not exist), exception code
02 (invalid data address) is returned. An attempt to write to a "read-only" register or a
reserved register is replied to with a Modbus error telegram (exception code 4 - device
failure). In this instance, the detailed internal error code that occurred on the last parameter
access via the holding registers can be read out via holding register 40499.
Table 6- 26
Example
11 h
06 h
00 h
63 h
55 h
66 h
xx h
xx h
The response returns the register address (bytes 2 and 3) and the value (bytes 4 and 5) that
was written by the higher-level controller to the register.
Table 6- 27
Example
11 h
06 h
00 h
63 h
55 h
66 h
xx h
xx h
6.8.3.5

Communication procedure

Procedure for communication in a normal case
Normally, the master sends a telegram to a slave (address range 1 ... 247). The slave sends
a response telegram to the master. This response telegram mirrors the function code; the
slave enters its own address in the telegram and so the slave identifies itself with the master.
The slave only processes orders and telegrams which are directly addressed to it.
Inverter cabinet units
Operating Instructions, 12/2014, A5E32923362A
Structure of a write request for slave number 17
Byte Description
0 Slave address
1 Function code
2 Register start address "High" (write register 40100)
3 Register start address "Low"
4 Register data "High"
5 Register data "Low"
6 CRC "Low"
7 CRC "High"
Slave response to the write request
Byte Description
0 Slave address
1 Function code
2 Register start address "High"
3 Register start address "Low"
4 Register data "High"
5 Register data "Low"
6 CRC "Low"
7 CRC "High"
Operation
6.8 Communication via RS485
239