Interesting JiffyDOS / C128 problem

Hi everyone,

 

I had someone email me an interesting question about a C128 with JiffyDOS.
He has two flat C128s, both working. He put JiffyDOS in one and it works
fine. He put JiffyDOS in the 2nd machine and got a black screen. He put the
original ROM back in the 2nd one and it booted fine again. He bought another
JiffyDOS ROM, installed it in 2nd machine and gets a garbage screen. He put
the original ROM back in and it works fine. So, it does seem that his second
C128 machine does not play nice with JiffyDOS.

 

The reason he emailed me was he saw the video I did on the VIC tower mod and
he wondered if his second C128 had that mod board and it was causing the
problem. I told him that the VIC tower mod board only had an effect on RAM
write timing, so it more than likely was not an issue in this case. It did
make me wonder what the problem might be though. 

 

My thoughts were that on the C128 CIA#2 is what talks to everything on the
IEC bus. The three IEC bus signals that come out of the CIA#2 also go though
some inverter/buffers. I'm just guessing but wonder if there is something
not quite right with CIA#2. A quick test would be to swap CIA#1 and CIA#2
and see if the problem changes. CIA#1 deals mostly with the keyboard,
joysticks, etc.

 

I have done some web searching and did not find a problem similar to this
mentioned. It makes me curious what the problem might be so I thought I
would mention it here to see if anyone had any ideas that might help him
out.

 

Thanks,

Jeff Birt