[Coco] Help with some HiRes CoCo 3 MMU settings

Robert Gault robert.gault at att.net
Wed Dec 7 21:13:14 EST 2016

Glen Hewlett wrote:
> Hi Robert,
> Thanks for the example code, It works fine for the FIRQ as it is, and I can hopefully use this to get my IRQ version working.  I noticed that in your Interrupt section the first thing you do is a “lda $FF93” is there a reason for reading the FIRQENR every time the interrupt is called?
> Just trying to learn…
> Thanks again.  Your code will help.
> Glen

I read $FF93 because I chose to use FIRQ instead of IRQ. Look at the beginning 
of the code where I installed FIRQ,pcr and turned on FIRQ with
lda #%00100000
sta $FF93

In the case of the GIME, reading $FF92 or $FF93 clears the interrupt. For cpu 
interrupts, you would clear the interrupt flags at $FF01, $FF03, $FF21, and 
$FF23; bit#7 (0-7) for each.


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