Configuring the fieldbus
7.6 Communication via RS485
Inverter with CU230P-2 Control Units
170 Operating Instructions, 11/2013, FW V4.6.6, A5E02430659B AG
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 7- 24 Slave response to the write request
11 h
06 h
00 h
63 h
55 h
66 h
xx h
0
1
2
3
4
5
6
Slave address
Function code
Register start address "High"
Register start address "Low"
Register data "High"
Register data "Low"
CRC "Low"
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.
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").
If the slave detects a logical error within a request, it responds to the master with an
"exception response". In this case, the slave sets the highest bit in the function code to 1 in
the response. If, for example, it receives an unsupported function code from the master, the
slave responds with an "exception response" with code 01 (illegal function code).
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