5 Apr
2010
5 Apr
'10
10:53 a.m.
Hi, All,
This has all been discussed over on the cbm-hackers list over the past
several months, but I've been fixing a couple of Static PET boards for
someone in Japan. The only thing that appears to be unique to one of
the boards is a 2316B in a Commodore-built 6540 adapter board (P/N
320076) and the 901447-12 ROM that's in it. There is no corresponding
ROM image on Zimmers.net (where the old funet archive lives), and this
ROM reads all zeros.
Does the machine work? If so, the ROM must be good (if the character
genereator was all 0's you'd get either totally black or totally white
charactoers (substitue whatever colour the CRT phosphor is for 'white',
of course).
One of the mask options with mask programmed ROMs (apart from the ROM
contents of course) was the polarity (active high .vs. active low) of the
enable signals. It's quite possible this ROM has at least one active-high
enable, whch means it will not read out in most programmers. Depending on
the programmer you migth be ableo t make up a little adapter to tie the
appropriate pin high or low and then read it out.
-tony