Re: "Less than" key and PET tape drive, again

From: Rhialto <rhialto_at_falu.nl>
Date: Wed, 8 Jan 2025 12:29:40 +0100
Message-ID: <Z35hpP3k6yMCqQnb_at_falu.nl>
On Tue 07 Jan 2025 at 19:38:23 -0500, Ethan Dicks wrote:
> On Tue, Jan 7, 2025 at 6:42?PM Ethan Dicks <ethan.dicks_at_gmail.com> wrote:
> > On Sat, Jan 4, 2025 at 5:57?PM Rhialto <rhialto_at_falu.nl> wrote:
> > > I think I asked here before if people knew about the effect on a PET
> > > ...where if you press the < key... while loading from tape, it prints < chars
> >
> > "Programming the PET/CBM" at the bottom of page 244:
> >
> > (See locations $E6AB ff.. In BASIC 2, for example).
> 
> That was the pointer I needed...  Here's the detect code...
> 00805  E69C  BD F7 E6           LDA CHAR-1,X
> 00806  E69F  D0 06              BNE CKIS1
> .
> .
> .
> 00810  E6A7  C9 FF       CKIS1  CMP #$FF
> 00811  E6A9  F0 0B              BEQ CKUT
> 00812  E6AB  C9 3C              CMP #$3C
> 00813  E6AD  D0 05              BNE SPCK
> 00814  E6AF  2C 11 E8           BIT PIAL1
> 00815  E6B2  30 02              BMI CKUT
> 00816  E6B4  86 A6       SPCK   STX SFDX
> 00817  E6B6  68          CKUT   PLA
> 
> So this bit of code updates or doesn't update SDFX depending on what
> keys are or are not pressed down and if PIAL1 has the high bit set or
> cleared.
> 
> Seems like it acts like a stuttering repeat depending on the state of PIAL1.

Thank you so much for finding this! Now I know I wasn't dreaming!

It even works in VICE, since it turns out that isn't some weird hardware
bug.

$ xpet -default -model 3032 -1 "some-random-tap-file.tap"

Virtually press "Play" using the pop-up menu on "Tape #1: 000".
Then press the < key.

Once the data on the tape starts the < key slowly repeats.
It seems to work better in that order than the other way around.

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert                            <rhialto/at/falu.nl>
\X/ There is no AI. There is just someone else's work.           --I. Rose


> -ethan

Received on 2025-01-08 13:00:01

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