Date   : Mon, 08 Sep 1986 09:10:43-EDT
From   : prindle@nadc.ARPA
Subject: Z80 cartridge for C64

The Z80 CP/M add-on cartridge for the Commodore 64 *will not* work on any C64
which contains the newer improved video (VIC II) chip.  The reason is that the
original video chip (used during about the first year of C64 production) had
a flaw in the derivation of the internal clocks and the processor clock from
the color clock input - this flaw caused the dot-clock to be in-phase with the
horizontal scan rate (a no-no for NTSC color character generation). The net
result was excessive chroma distortion of the characters in most color combi-
nations on a TV set or NTSC monitor.

It took Commodore a while to realize what the problem was, but eventually they
fixed it.  Unfortunately, the phase relationship between the processor clock
and the dot clock was irrevocably altered, and all CP/M cartridges (which
worked with the old chips) suddenly croaked.  I think the Federal Trade
Commission considered this a massive enough screw-up on Commodore's part to
order them to refund the purchase price on any and all CP/M cartridges, which
they did and are still doing.

As the proud owner of one of these, your only alternatives are:

  1. Find a C64 owner with one of the old VIC II chips (display red characters
     on a black background and look at the output on a TV set - if you can't
     read every other character, it's the old chip.  If the display is quite
     readable, it's the new chip) and swap chips with him.  He'll enjoy the
     better video; your CP/M cartridge will work.  However, unless you're using
     a "separated" video monitor (e.g. C= 1702), your eyes will suffer!

  2. Contact Commodore and ask how to get your money back!

Sincerely,
Frank Prindle
Prindle@NADC.arpa