IDEC SmartAXIS Touch FT1A Series, Руководство пользователя

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6 Ladder Program
A-8
SmartAXIS Touch User’s Manual
This section describes details on ladder program processing, instruction execution times, and the byte count for
instructions.
6.1 Processing in One Scan
While the Touch is running, the Touch performs operations repeatedly such as input refreshing, ladder program
processing, and error checking. A
scan
is the execution of all instructions from the first line of the ladder program to
the END instruction. The time required for this execution is referred to as one
scan
time. The scan time varies with
respect to program length.
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).
6.2 Executing Program Instructions
During the scan time, the ladder program is executed sequentially from the top to the bottom except when interrupt
programs are executed. One scan time of a ladder program is approximately equal to the total of execution time of
each instruction.
For the instruction execution times, refer to “6.4 Execution Times for Instructions” on page A-9.
6.3 Breakdown of END Processing Time
With the Touch, processing that occurs outside ladder program processing is referred to as END processing. This
includes the processing for I/O refreshing and error checking.
6 Ladder Program
When the processing time for one scan exceeds the specified time, a watch dog 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.
Item END Processing Time
Housekeeping (built-in I/O service) 5 msec min.