Communication processor and Modbus TCP
13.9 Legacy Modbus RTU communication (CM/CB 1241 only)
S7-1200 Programmable controller
1278 System Manual, V4.2, 09/2016, A5E02486680-AK
Table 13- 152 MB_MASTER execution condition codes (Modbus protocol errors)
1
8381 01 Function code not supported
8383 02 Data address error or address outside the valid range of the
DATA_PTR area
Data diagnostic code value not supported (function code 08)
Function code in the response does not match the code in the request.
8388 - The slave response to a write request is incorrect. The write request
returned by the slave does not match what the master actually sent.
In addition to the MB_MASTER errors listed above, errors can be returned from the underlying PtP communication
MB_SLAVE (Communicate using the PtP port as Modbus RTU slave)
Table 13- 153 MB_SLAVE instruction
MB_ADDR:=_uint_in_,
NDR=>_bool_out_,
DR=>_bool_out_,
ERROR=>_bool_out_,
STATUS=>_word_out_,
MB_HOLD_REG:=_variant_inout_);
The MB_SLAVE instruction allows your pro-
gram to communicate as a Modbus slave
through a PtP port on the CM (RS485 or
RS232) and CB (RS485). When a remote
Modbus RTU master issues a request, your
user program responds to the request by
MB_SLAVE execution. STEP 7 automatically
creates an instance DB when you insert the
instruction. Use this MB_SLAVE_DB name
when you specify the MB_DB parameter for
the MB_COMM_LOAD instruction.
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