Communication processor and Modbus TCP
13.5 Modbus communication
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1205
8280 Negative acknowledgement when reading module. Check the input at the PORT parameter.
This can be caused by the loss of a PROFIBUS or PROFINET distributed I/O module, either
by a station power or communication loss or a module pull.
8281 Negative acknowledgement when writing to module. Check the input at the PORT parameter.
This can be caused by the loss of a PROFIBUS or PROFINET distributed I/O module, either
by a station power or communication loss or a module pull.
Table 13- 79 Modbus_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 Modbus_Master errors listed above, errors can be returned from the underlying PtP communication
Note
Setting the maximum record length for Profibus communication
When using a CM1243
-5 Profibus Master module to control an ET 200SP or ET 200MP
Profibus device that uses an RS232, RS422, or RS485 point
-to-point module, you need to
explicitly set the "max_record_len" data block tag to 240 as defined below:
Set "max_record_len" in the Send_P2P section of the instance DB (for example,
"Modbus_Master_DB".Send_P2P.max_record_len) to 240 after running
Modbus_Comm_Loa
d.
Explicitly assigning max_record_len is only necessary with Profibus communication; Profinet
communication already uses a valid max_record_len value.
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