Timer? input question

[Carl Ijames]

>What is the reason for a section of code to do something like this?  I'm 
>hypothesizing that it is reading a timer from outside the HC11, and it 
>wants to compare whatever is at $14a6 & $1486, without getting interrupted 
>and the lda & nop are just for a little delay to read or time to twiddle 
>bits or something.  Am I in the ballpark?

My guess is that either the hardware register is double buffered so they 
read it twice to get the latest data (and for some reason this is slow so 
they need the nop to let the register get ready to be read again), or maybe 
reading it clears the register so they get only the data that came in 
during the time needed to execute one nop (and if an interrupt happened 
during this it would screw it all up so that's why they di/ei).  Anyway, 
just a guess.

>di
>ldaA    L14A6
>nop
>ldX     L14A6
>ldaA    L1486
>nop
>cmpX    L1486
>ei
>bne     @18

Regards,
Carl Ijames     ijames at netaxs.com

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