Re: Patching in a CBM disk drive connection in a C64 case.

From: William Levak <wlevak_at_SDF.ORG>
Date: Mon, 4 Apr 2022 19:21:47 +0000 (UTC)
Message-ID: <Pine.NEB.4.64.2204041920110.26653_at_sdf.org>
The problem is described in Synertek's 6522 data sheet.

On Sun, 3 Apr 2022, Rhialto wrote:

> On Fri 01 Apr 2022 at 14:30:13 -0500, Jim Brain wrote:
>> http://www.zimmers.net/anonftp/pub/cbm/faq/trivia/cbm-trivia-08.txt
>> (question $07b)
>
> from that: "We early PET/CBM freaks knew, from playing music, that there
> was something wrong with the 6522's shift register:  it interfered with
> other functions.  The rule was:  turn off the music before you start the
> tape!  (The shift register was a popular sound generator)."
>
> Do we already know why the shift register interfered with the tape?
>
> and, to remind people, do we already know why pressing the < button
> while loading / scanning the tape for something to load would print
> < characters to the screen if there was a signal on the tape?
>
> Neither are emulated in VICE (I think I tried it once) so it isn't
> something that trivially occurs...
>
> Also, Compute #3, march/april 1980, mentions that sound
> doesn't work if you have C2N #2 plugged in. Page 88:
>
> "NO CB2 SOUND?
>
> Larry Isaacs
>
> Some of you may have been unable to get the CB2 Sound, described in last
> month's RAMBLIN', to function. Fortunately the most likely cause has a
> very simple solution. Unplug the external cassette from the rear of your
> PET. Having an idle cassette plugged into that cassette port grounds the
> CB1 line on the 6522 IC in the PET. Grounding CB1 unfortunately stops
> the shifting of the shift register used to generate the CB2 Sound. I
> also checked a Synertek 6522 (PETs use MOS Technology) and found that it
> had the same problem.  It appears that this is inherent in the design of
> the 6522, so keep it in mind when using the shift register for output.
>
>
> -Olaf.
> -- 
> ___ "Buying carbon credits is a bit like a serial killer paying someone else to
> \X/  have kids to make his activity cost neutral." -The BOFH    falu.nl_at_rhialto
>

wlevak_at_sdf.org
SDF Public Access UNIX System - http://sdf.org
Received on 2022-04-04 22:00:08

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