In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Sparks-R-Fun wrote:

[QUOTE="Peter Verkaik"] The sequence to write to the DDR registers, once M is set, is:
MOV W,DDRACOPY ;any DDR copy register
MOV !RA,W

If an interrupt occurs inbetween those 2 instructions, and the interrupt
would update direction bits for port RA, then the interrupt update becomes
undone.
The function DDRupdate in library Portpin.h inserts an extra clockcycle
when an RTCC rollover would occur inbetween those 2 instructions.
As a result, the interrupt occurs before the MOV W,DDRACOPY instruction,
so if the interrupt update the DDR registers, the change is maintained. [/QUOTE]Edge triggered interrupts might still experience a problem.

- Sparks

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