The C128 Keyboard IO controller is...

From: Bo Zimmerman <>
Date: Thu, 16 Jul 2015 01:34:50 -0500
Message-ID: <>
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.

- Bo

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Received on 2015-07-16 07:00:08

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