Mitsubishi Electric melsec q00ujcpu User Manual page 57

(b) Initial scan time
Initial scan time is the execution time of initial execution type program.
When multiple programs are executed, the initial scan time will be the time required for completing
all the initial execution type program execution.
1) Initial scan time storage location
The CPU module measures the initial scan time and stores it into the special register (SD522 and
SD523).
The initial scan time can be checked by monitoring SD522 and SD523.
SD522
Example
time is 3.4ms.
2)
Accuracy and measurement of the initial scan time
Accuracy of the initial scan time stored in the special register is
Even if the WDT instruction (instruction that resets the watchdog timer) is executed in the
sequence program, the measurement of the initial scan time continues.
3) Execution of an interrupt program or fixed scan execution type program
When an interrupt program or fixed scan execution type program is executed before completion of
the initial execution type program execution, the execution time of the executed program will be
added to the initial scan time.
(3) Precautions on programming
Initial execution type programs do not support the instructions that require several scans (instructions
with completion device).
SEND, RECV, and similar instructions
Example
2 - 18
SD523
Stores the initial scan time of 1ms or less (unit: s).
Stores the initial scan time. (unit: ms).
Figure 2.21 Initial scan time storage location
If the stored values in SD522 and SD523 are 3 and 400 respectively, the initial scan
0.1ms.