SmartAXIS Touch User’s Manual A-13
7 FBD Program
Appendix
This section describes details on FBD program processing, FB execution time, and the byte count for FBs.
7.1 Processing in One Scan
While the Touch is running, the Touch continue to perform operations such as input refreshing, FBD program
processing, and error checking. The execution of such a set of processing is defined as a
scan
. The time required for
this execution is referred to as one
scan time
. The scan time varies depending on the created FBD program.
The current value of the scan time is stored to special data register D8023 (scan time current value), and the
maximum value of the scan time is stored to special data register D8024 (scan time maximum value).
7.2 FBD Program Processing
In FBD programs, all of the FBs connected to the output FB (digital output FB or internal relay FB) are executed
sequentially from the input FBs. The FBD program processing time in one scan is approximately equal to the total of
execution time of each FB.
For the execution time of each FB, refer to “7.4 FB Execution Time” on page A-14.
7.3 Breakdown of Scan End Processing Time
After processing the FBD program, the Touch processes housekeeping operations at the end of each scan. It is
referred to as Scan End processing. This includes the operations such as I/O refreshing and error checking.
7FBD Program
If the processing time for one scan exceeds the specified time for the watchdog timer, a watchdog timer
error occurs and the system is reset. For details on the watchdog timer, refer to Chapter 3 “4.17 Watchdog
Timer Setting” on page 3-98 and Chapter 5 "Special Functions" - "Watchdog Timer Setting" in the
"SmartAXIS Pro/Lite User's Manual".
Item Processing Time
Scan End Processing 5 msec min.
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