Re: Dating a C-64 board

From: Nicolas Welte (
Date: 1999-04-18 11:54:16

Ethan Dicks wrote:
>     ASSY 326298
>     REVB (C) 1982
>     COMMODORE 64

The ASSY number is the key to identify each board. The C64 service
manual (also online on funet, I think) lists this number as 'original
board'. There also is a version A, B, B-2, B-3 and E board. The
respective numbers are 250407, 250425, 250441, 250446, 250469. The E
board exists in two different revisions, one with a discrete color RAM
chip (rev 3 and rev 4), the other without one (rev B).

The schematic of the original board suggests that there is a PAL/NTSC
jumper, it should be a jumper wire like in the version A board that can
be put either on location E2 or E3. The board layout shows an empty
space near U29 in the video cage, maybe this is where the jumpers are.

> Right.  The ROMs page on funet mentions that the RS-232 constants assume
> a 1.0Mhz CPU (my guess is that they forgot to update the numbers from
> the V(I)C-20.  I used to use this with a VIC-modem, so at least at 300
> baud, it's close enough.

The early 6567 chips also had a different timing that looks like it was
made for exactly 1MHz system clock. This is also the clock frequency of
the Ultimax computer which uses a 6566 VIC-II chip. Maybe they made a
last minute change in the C64 for unknown reasons, and the video chip
and the ROM were left configured for 1MHz. And I think the VIC-20 runs
at significantly higher clock speed, perhaps 1.2 MHz. I forgot ;-)

It's a pity that you don't have your original C64 anymore. There's
always the search for early chips to explore funny bugs. I think Andreas
Boose wanted to know once if the reset bit, that is disabled in all
known VIC-II chips is perhaps active in very early versions. Perhaps you
could try it on your machine?


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