At 01:24 PM 4/15/99 -0700, Clay wrote:
>
>Well this is potentially embarssing... No I'm not-- is there a
>dedicated location to clear? It makes sense- it sure looks like my ISR
>is running because I'm getting a steady display. I guess it could just
>be looping in the ISR forever and not making it back out to the "zoom"
>part of the main code. Excellent advise... Danke!
>(And MAME probably doesn't really "latch" the IRQ input, so that might
>jive with it working OK there...)
Yes there is. When jeff and I were trying to get our game code to run on
real hardware...it worked in MAME but not on the real hardware. As it turns
out MAME does not emulate the clearing the IRQ counter. Basically MAME must
just handle the ISR differently.
Now. I don't know what the dedicated location is on Tempest (we're writing
new games for Space Duel hardware), and I don't have my schematics handy to
check, but if you look you'll see that there is a counter off the IRQ of
the 6502. That counter must be cleared or you will be stuck in the ISR
forever. The counter clear is just an address decode, so to clear it you
just "sta INTACK", where INTACK is the hex location for the counter clear.
Get that in you ISR, and you're closer to being in business!
Enjoy,
-Anders.
Received on Thu Apr 15 15:41:58 1999
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