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Process interfacing via an automation system (PLC, PC)
9.4 Control with FB 79
You should therefore process the "DONE" and "ERROR" parameters at each block call. If
the transfer was successful, "DONE" = "TRUE" is set. However, this only means that the
transfer between the optical reader and the FB (CPU) was error-free. To find out whether the
DMC processing was successful, you will need to process bits "READ" (bit 3), "MATCH"
(bit 4) and "N_OK" (bit 5) in the status byte of the optical reader. In this case, refer to the
following table for the behavior of FB 79. Always process the "ERRCODE" parameter to get
warnings from the FB.
Table 9- 49
Effects of the behavior of the optical reader on the FB 79
Behavior of the optical reader
The code could not be decoded.
The code was successfully decoded; how-
ever, you have not set any specifications.
The code was successfully decoded but
does not match your specifications.
The code was successfully decoded and
matches your specifications.
Process the data entered in "RECV" before the next trigger; otherwise, the consistency of
this data cannot be guaranteed. At the same time, you should also process the "LENGTH"
parameter because the receive area is written only up to this length.
You can abort an active read job by calling FB79 with "COMMAND = W#16#0000".
If an error occurs when processing a job or when a current read job is canceled, "ERROR =
TRUE" is set. In this case, the "ERRCODE" parameter contains an ID indicating the cause of
the error. FB 79 writes "B#16#00" to the "RECV" target area.
Startup behavior
If an error occurs ("ERRCODE <> DW#16#0000 0000"), you need to initialize the FB once
with "RESET=TRUE" after calling an interrupt OB (for example, OB 82) and after a "STOP-
RUN" change on the CPU. Please include a suitable first call in your user program.
9.4.5.4
Error information
If an error has occurred, the "ERROR" parameter is set to "TRUE". The precise cause of the
error is then displayed in "ERRCODE". There are also warnings for which "ERROR" is set to
"FALSE". They indicate error situations that do not cause the current job to be canceled.
If "ERRCODE" <> DW#16#0000 0000" following an FB call, you will need to call the FB
again with "RESET = TRUE" to reset the error information in the FB.
Note
Acknowledging the error of the optical reader
By calling the FB with "RESET = TRUE", you only acknowledge error displays of the FB. To
acknowledge errors of the optical reader (e.g. "Transmit error"), you must set the "RES" bit
of the control byte.
150
Effect on FB 79 ("RECV" target area)
FB 79 enters the string set in the "ReadErr" parameter.
FB 79 enters the result string.
FB 79 enters the string set in the "MatchErr" or "FilterMsg" parameter if the
Match or Filter function is set. If both these functions are selected, FB79
enters the string set under "MatchErr".
FB 79 enters the result string.
Operating Instructions, 05/2019, C79000-G8976-C494-02
SIMATIC MV500
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