Communication processor and Modbus TCP
12.5 Modbus communication
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
755
Table 12- 72 MB_MASTER execution condition codes (Modbus protocol errors)
1
Function code not supported
8383 02 Data address error or address outside the valid range of the
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 via the PtP port as Modubus slave) instruction
Table 12- 73 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
program 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.
Table 12- 74 Data types for the parameters
MB_ADDR IN V1.0: USInt
V2.0: UInt
The station address of the Modbus slave:
Standard addressing range (1 to 247)
Extended addressing range (0 to 65535)
MB_HOLD_REG IN Variant Pointer to the Modbus Holding Register DB: The Modbus holding
register can be M memory or a data block.
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