Mitsubishi Electric MELSEC-Q00U(J)CPU User Manual page 562

(3) Replacing the COM instruction
If the COM instruction is used, add subroutine calls for P10 and P11 before and after the COM instruction. (P10
and P11 are pointers shown in the program examples in (2).) When SM775 is on (Executes refresh set by SD778)
and also the 0 bit of SD778 is off (Do not execute I/O refresh), replacement of the instruction is not necessary.
(a) Program before replacement
(b) Program after replacement
560
Selection of refresh processing
during COM instruction execution
Selection of refresh processing
during COM instruction execution