Communicating with the PLC
7.2 MODBUS communication
SINAMICS V20 Converter
Operating Instructions, 10/2019, A5E34559884-012
185
Response for unsuccessful write operation - write request still not completed
20 h
0001 h
2F00 h
0004 h
3
4,5
6,7
8,9
Number of following data bytes (20 h: 32 bytes
16 regis-
ters)
40601: DS47 Control = 1 (request is processed)
40602: Function 2F h(47), response length 0 (fault)
40603: Error code: 0004 Response Not Ready (response has
xx h
10
CRC "Low"
Exception Responses
If an error is detected through the MODBUS processing, the slave will respond with the FC
of the request, but with most significant bit of the FC high and with the Exception Code in the
data field. However, any error detected on the global address 0 does not result in a response
since all slaves cannot respond at once.
If an error is detected within the received message (for example, parity error, incorrect CRC
and so on), then NO response is sent to the master.
Note that if a request with FC16 is received which contains a write that the converter cannot
perform (including write to a zero entry), other valid writes will still be performed even though
an exception response is returned.
The following MODBUS Exception Codes are supported by SINAMICS V20:
01 Illegal function code The function code is not supported – only FC3, FC6 and
An invalid address was queried.
An invalid data value was recognized.
04 Slave device failure An unrecoverable error occurred while the device was
The table below shows the cases in which an Exception Code is returned:
Read registers, which are out of boundary
Write register, which is out of boundary
Read request of too many registers (>125)
Write request of too many registers (>123)
Write to a read-only register
Write register, error in parameter access
Read register, error in Parameter Manager
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