Re: The C128 Keyboard IO controller is...

From: Greg King <>
Date: Thu, 16 Jul 2015 20:00:58 -0400
Message-id: <>
On 2015-07-16 2:34 AM, Bo Zimmerman wrote:
> 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 of 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, the CP/M BIOS does its own keyboard scanning; and, it sends the 
signals (from one port to the other port) in the opposite direction than 
the Kernal does it.

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Received on 2015-07-17 02:00:07

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