stuff from Classic Computing

From: Nicolas Welte; address is valid for replies (Re:) only! (
Date: 2002-10-01 00:28:09


on Saturday I attended the Classic Computing meeting near Heilbronn, 
Germany and I had my PET 2001 with me. This was the first time I had this 
machine running a whole day, and it worked very well. It was also the first 
heavy duty test for the hardware I built to replace the old 6540 and 6550 
chips, and all three boards worked very well: the system RAM/ROM 
replacement board, and the two little video RAM and ROM replacement boards. 
I also had a Userport video adaptor and Marko's C2N232 device with me.

This was also the first time I used replacement I/O chips: Instead of the
original 6520s I used two 68B21 that I bought just some weeks ago. I know
we discussed it several times that the 6821 and the 6520 are pin and
register compatible, so a 6821 should be a direct replacement, but nobody
ever confirmed that this works. I didn't have any problems with them, the
keyboard worked fine, the datasette ports and the IEEE port also worked
fine. And instead of the original 6522 from 1978 I used a model from 1984,
just to make sure noone damages it by abusing my PET.

I heard some stories from Plus/4 users who "developed" a new kind of 8501
CPU replacement. They use a 8502 on an adaptor, and reprogram the KERNAL to
be aware of the different I/O port bit mapping! I think the bit that is
missing on the 8502 is connected to the serial port, so without the KERNAL
patches no serial devices can be used.

I also had the opportunity to copy the ROMs of a small screen PET 4016 onto
my FlashROM expansion, and could then use this copy in my static PET 2001.
Now I have a fully working set of BASIC 4.0 running in my 2001, which I was
not able to to with the ROM images from Funet before. Now I wonder why this
was so, because my new copy matches the one from Funet perfectly (revised
BASIC 4.0 and non-CRTC editor for graphic keyboard). The only difference is
an extra option ROM that I also copied, but I don't have an idea what it
does. It might be related to the fact that this PET 4016 had a keyboard
with japanese letters on it, but the character ROM is just the normal one.


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