Mitsubishi Q2ACPU, User Manual

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12. OVERVIEW OF PROCESSING PERFORMED BY THE QnACPU
(4) Initial scan time
(a) This is the execution time of an initial execution type program.
If multiple initial execution type programs are to be executed, it is the time
required to complete execution of all these programs.
(b) The QnACPU measures the initial scan time and stores it in special registers
SD522 and SD523.
*1
The initial scan time can be checked by monitoring SD522 and SD523.
Example:
If "3" and "400" are stored in SD522 and SD523 respectively, the initial scan time
is 3.4ms.
*1 The accuracy of each scan time stored in the special registers is 0.1ms. Note that, even if a
watchdog timer (WDT) reset instruction is executed in the sequence program, measurement
of the initial scan time is continued.
(5) Initial execution monitoring time
This is a timer for monitoring the execution time of initial execution type programs; no
default value is set.
To monitor the execution time of an initial execution type program, a value can be set
within the range of 10ms to 2000ms in "PLC RAS" in the parameter mode. (Unit: 10
ms)
If the initial scan time exceeds the set initial execution monitoring time, a "WDT
ERROR" occurs and the QnACPU stops its operation.
POINT
An error may be generated in the range of 0 to 10ms in measurement of the initial
execution monitoring time.
Because of this, if the initial execution monitoring time (t) is set as 10ms, a WDT
ERROR will occur when the initial scan time exceeds the limit within the range of
10ms t 20ms.