Date   : Wed, 11 Feb 1987 21:21:01-EST
From   : prindle@nadc.arpa
Subject: re: CP/M on the Commodore 64

The reason that the CP/M cartridge works on some 64s and not on others is that
newer 64s have an improved VIC II chip which produces proper NTSC video (the
old one had a bug and divided a clock by 64 instead of 65, or something like
that, which produced garbled color video).  The newer chip produces a slightly
different (1 or 2 percent) processor clock timing and the CP/M cartridge fails
to operate correctly.  The only cure is to use an older VIC II chip - if you
are using a Commodore 1701/1702/1802/1902 monitor with the separated video
input, the old chip looks as good as the new one.  Only the composite video is
screwed up.  Thus, if you have a friend with a C64 with the old VIC II chip but
no CP/M cartridge, do both of you a favor and trade chips with him - he gets a
better composite display if that matters, and you get a working CP/M cartridge.
The VIC II chip is the large chip to the left side under the metal "can" - it
has a blob of heat-sink compound on the top that a spring presses on when the
cover is replacd.
Sincerely,
Frank Prindle
Prindle@NADC.arpa