Craig Steiner wrote:
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....This is also a perfect use for CLR EA and SETB EA which lets you quickly disable/enable all interrupts. So just execute the CLR EA before modifying the global variable and SETB EA after you're done.....

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To be even safer, you can also do:

push  IE  ;In case EA has already been disabled
clr   EA
.
;Critical Region
.
pop   IE