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Communication in SIMATIC S7-300/400/1200/1500
11.6 Working with the function block
Figure 11-7
As shown in the graphics, a command mailbox always consists of a command code (Int) and
four bits (Bool). A command is set by entering the desired command code in the
"i_CMD_CODE" parameter and setting the respective command trigger "bo_CMD_TRIGGER".
The status bits "bo_CMD_InProgress" (command being processed), "bo_CMD_FinishedOk"
(command finished without errors) and "bo_CMD_FinishedError" (command rejected or
finished with error) can be evaluated in the user program.
In addition, the three command mailboxes are managed and processed according to priority.
CMD1 has the highest priority, CMD3 has the lowest priority. If all three command mailboxes
are triggered simultaneously by the user program, for example, the function block initially
processes CMD1, then CMD2, and finally CMD3. Cyclic triggering of command mailbox 3 is
also interrupted by intermediate sending of a command in mailbox 2 or 1 for processing of the
respective command.
Note
Cyclic triggering of the CMD1 command mailbox makes it impossible to send commands in
mailbox 2 or 3.
A summary of all existing command codes can be found in chapter →Command lists
(Page 101).
The following equation for generation of a corresponding command code applies to the reading
of data records from the SIWAREX to the data block:
108
CMD command mailboxes
Operating Instructions, 08/2019, A5E33715669A-AD
SIWAREX WP321
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