Mitsubishi MELSEC Q Series Reference Manual page 516

APPX - 20
POINT
(1) The programmable controller CPU performs only one of the above operations
during END processing.
If the programming tool and modules simultaneously access the
programmable controller CPU, the newly-requested processing has to wait
until the current processing ends. In this case, the number of scans required
for the processing increases even more.
(2) If the increase in scan time affects the operations of the programmable
controller CPU, access the CPU module multiple times by dividing the points.
APPENDICES
APPX - 20