RE: Commodore 8296GD

From: MiaM <>
Date: Fri, 26 May 2017 19:59:21 -0700 (PDT)
Message-ID: <>
>> One more thing - the register is not cleared by a reset. So if you map
>> out the BASIC ROM, then press the reset switch, the computer will not
>> restart because the BASIC ROM is still mapped out. Only switching it
>> off and on will work. Quite sloppy design, because resetting the
>> computer while performing some graphics operation may render it
>> unusable unless physically turned off (losing all RAM contents).
>The register 74LS174 has a /CLR input at pin 1. I see a track near this
pin. On the other end of this track is >pin 2 (/RES) of 6545. So the
question is, isn't that connected?

The 8296 has two different reset lines, one for the CRTC and another for
everything else. Both goes low for a while when you turn the power on, but
the reset button is only connected to the line that doesen't reset the CRTC.
That's the reason why you can see the screen contents for a short while
after you have pressed the reset button.

P.S. isn there any progress on the reverse engineering of this card? I'd
really like to build one myself.

In case you wounder how I ended up on this list: I just aquired a PET 600,
which is basically a rebranded 8296. It has swedish (same as finnish?) ROM's
for keyboard layout and character generator, but the keyboard were missing.

I also got an empty CBM II keyboard case. Currently I have rewired the
matrix on an old "FACIT" terminal keyboard, made by Cherry (black MX, yay).
It's interesting that the keyboard decode routines in ROM actually support a
few more keys than the actual keyboard has. As my old terminal keyboard had
plenty of extra keys I've wired up those extra keys too. For example I'm
able to switch between the two character sets in both directions e.t.c. .
Maybe I should make a new PCB that fits in the CBM II keyboard case and use
the switches from this terminal. However I'm not sure enough keys will fit,
and it feels lika a really bad idea to cut out a bigger hole for the keys in
the case. The CBM II machines are probably rather rare as I understand it.

I currently only have a datasette as storage, but some kind of plan involves
building some kind of IEEE 488 disk drive emulator, or maybe a general
emulator of all kinds of C= IEEE hardware. (AFAIK there were disks, printers
and a rare accoustic modem. With an emulation of a "modem" the PET could be
used as a terminal for for example a Linux computer.

I'm also known for making lots of plans and seldom actually go through and
finish my projects.

I got hold of some old electronic junk that contains a bunch of edge
connectors that physically fits the PET but the connectors are "single
sided" in the sense that it short circuits the upper and lower pins in each
position, thus only usable for the datasette ports. The connectors are wider
than the datasette port, and I haven't got any of those "key" things, so you
have to cut the connectors and also make some kind of key to be sure it's
not inserted incorrectly. Is there any interest for such connectors? The
could probably be used with C2N232 with some effort, but otherwise they are
probably rather useless.

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Received on 2017-05-27 04:00:02

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