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2010-09-07 12:27

TWW

Registered: Jul 2009
Posts: 541

$dc0d madness

how come a lot of people set up their raster IRQ's like:

lda #$01
sta $d01a
lda #$7f (?)
sta $dc0d

and not just simply:

ldx #$00 // I believe 0 = mask and 1 = don't mask but it isn't specified in the prog.ref.manual...
stx $dc0d // Mask out all CIA#1 IRQ's
inx
stx $d01a // Mask out all VICII IRQ's minus raster compare

Where does this "#$7f" come from?

or have i missed some kind of importaint point here?

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2010-09-09 07:20

TWW

Registered: Jul 2009
Posts: 541

Quote: Quoting TWW
What I find interesting is that SEI itself only inhibit activation of IRQs but don't stop them from setting bits high in $d019/$dc0d even during a sei-cli.

SEI affects CPU only, your interrupt sources are two CIAs and VIC-II. 6510 doesn't generate any interrupts (except BRK which doesn't care about SEI) by itself, it just reacts to an external signal.

Thank you. This confirms my thoughts further.

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