Siemens SINAMICS G120 CU240E-2 - Communication Procedure

Connection to a fieldbus
6.4 Communication via RS485
Inverter with CU240B-2 and CU240E-2 Control Units
152 Operating Instructions, 07/2010, FW 4.3.2, A5E02299792B AA
Table 6- 33 Structure of a write request for slave number 17
Example
Byte Description
11 h
06 h
00 h
63 h
55 h
66 h
xx h
xx h
0
1
2
3
4
5
6
7
Slave address
Function code
Register start address "High" (write register 40100)
Register start address "Low"
Register data "High"
Register data "Low"
CRC "Low"
CRC "High"
The response returns the register address (bytes 2 and 3) and the value (bytes 4 and 5) that
was written to the register.
Table 6- 34 Slave response to the write request
Example
Byte Description
11 h
06 h
00 h
63 h
55 h
66 h
xx h
xx h
0
1
2
3
4
5
6
7
Slave address
Function code
Register start address "High"
Register start address "Low"
Register data "High"
Register data "Low"
CRC "Low"
CRC "High"
6.4.3.5 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, and
the slave enters its own address in the telegram, which enables the master to assign the
slave.
The slave only processes orders and telegrams which are directly addressed to it.
Communication errors
If the slave detects a communication error on receipt (parity, CRC), it does not send a
response to the master (this can lead to "setpoint timeout").