Re: The C128 Keyboard IO controller is...

From: David Wood <>
Date: Thu, 16 Jul 2015 07:09:05 -0400
Message-ID: <>
Does CP/M use the same CIA for interrupt timers?  This also doesn't make a
lot of sense, using an NMI for the periodic interrupt but it would make
sense if the c128's not scanning the keyboard at all during CP/M operation.

I lean toward Groepaz's theory more than my own, but I thought I'd post my


On Thu, Jul 16, 2015 at 4:38 AM, <> wrote:

> On Thursday 16 July 2015, 01:34:50 Bo Zimmerman <> wrote:
> > I often hesitate to post my personal discoveries to this list, fearing I
> > will say something obvious, like "Hey guys! Did you know that if you
> > remove the 6581 chip, the C64 stops making sound????"
> >
> > However, this is strange enough that I will take a chance.
> >
> > Hey guys! Did you know that it appears like a different CIA chip handles
> > keyboard signals, depending on whether or not the Z80 is operating?
> >
> > I boot CP/M on my flat C128 rather often, and one day I booted into it
> > to discover that the keyboard no longer worked.  The keyboard worked
> > fine in regular c64 and c128 mode.   I was also seeing strange
> > intermittant behavior on the IEC bus at the same time.  I decided it
> > must be a twitchy CIA.  Thank the Makers that both the CIAs in the flat
> > C128 are socketed.  I simply swapped them, which should take care of bad
> > CIA and poorly seated chip problems.  Well, to my surprise, when I
> > booted it next, the keyboard worked fine in CP/M, and did not work at
> > all in c64/c128 modes.  I then replaced the bad CIA (it was the one
> > closest to the user port), and everything is good.
> >
> > I'm perusing the schematic, and it makes no sense to me.  But there it
> is.
> >
> > I apologize if this is common knowledge, but it surprised the heck out
> > of me.
> perhaps CP/M scans the keyboard in a different way, which doesnt work on a
> partially broken CIA?
> --
> Die [weiber] wollen entweder a) ficken oder b) sich darüber beschweren,
> dass
> männer nur ans ficken denken
> <Graham/Oxyron>
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Received on 2015-07-16 12:00:07

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