Communication with SIMATIC S7-1200
11.2 Communication via Modbus
SIWAREX WP251
Manual, 12/2015, A5E37203357A
195
Corresponding command codes must be sent in order to execute commands and to read
and write data records in the Modbus buffer memories. These are described in more detail in
chapter → Command lists (Page 179). The following tables list the Modbus registers used to
process these commands:
Table 11- 3 Command mailbox 1: Highest priority
Code of command to be executed
CMD1_TRIGGER Trigger for starting the command USHORT 911
0=job running; 1=job finished (1 cycle)
0=no error; <>0=error code
Table 11- 4 Command mailbox 2: Average priority
Code of command to be executed
CMD2_TRIGGER Trigger for starting the command USHORT 921
0=job running; 1=job finished (1 cycle)
0=no error; <>0=error code
Table 11- 5 Command mailbox 3: Low priority
Code of command to be executed
Trigger for starting the command
0=job running; 1=job finished (1 cycle)
0=no error; <>0=error code
The method for reading registers depends on whether they belong to the writable data
records (DR 3 to DR 29) or can only be read as current values (DR 30 to DR 39).
If you wish to read the registers from the data records DR 3 to DR 29, you must first export
these as a complete data record to the internal output buffer.
All Modbus registers of the individual parameters can be found in chapter → Scale
parameters and functions (Page 57).
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