Yes, The /NMI line is permanently pulled HIGH via a resistor, so it is forced into the inactive state. It is, however, connected to J4 pin 24 - so it can be connected to something from the outside world. As Steve has already stated, all of the internal devices are connected to the maskable interrupt line (/IRQ). Dave On Thu, 4 May 2023, 02:05 Steve Gray, <sjgray_at_rogers.com> wrote: > Hi Bo, > > The CA1 line generates IRQ only. The NMI is not actually connected in the > PET. You may be able to use IRQ but remember that multiple things generate > IRQ's, such as the CRTC vertical retrace, and cassette data. > > Steve > > > > On Wednesday, May 3, 2023 at 07:39:28 p.m. EDT, Bo Zimmerman < > bo_at_zimmers.net> wrote: > > > > My original program is indeed assembly, but much more complex. I thought > a nice short BASIC program might reveal my problem more clearly. Here's > the identical program in assembly -- with the exact same results. I have a > multimeter sitting on the CA1 line, so I can see it go high->low, and also > see the lack of activity. > > *=$1000 > lda #<NMIH > sta $94 > lda #>NMIH > sta $95 > lda #0 > sta $e84d > lda #$82 > sta $e84e > NOSP jsr $ffe1 > bne NOSP > rts > NMIH inc $8000 > rti > > > > Sorry, I'm typo-ing all over my emails today. The $ea4e should be $e84e. > I had it right in the code I'm running though, so again-- I don't > understand why my screen character does not change. > > Thanks again, > > - Bo >Received on 2023-05-04 09:00:03
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