Anyone have an image of a Japanese PET chrgen ROM 901447-12?
ethan.dicks at gmail.com
Mon Apr 5 13:20:07 CDT 2010
On 4/5/10, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> Does the machine work?
Yes, video works except for the CHRGEN ROM. If it worked in its
"normal" space, I'd just type chars to validate the Katakana mapping
> 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).
That's exactly it... all chars that are in "normal video" are blank,
and all chars in inverse video are white (exactly as expected since in
PETs unlike C-64s, normal/reverse video is handled in hardware, not
with a 4K CHRGEN ROM).
> 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.
I am not reading this in a programmer - the footprint from the adapter
is for the 6540, not JEDEC, and I have no programmer that knows what a
6540 is (the ROM on the adapter is a 2316, but it's soldered in place
and I was trying not to remove it to minimize the risk to the ROM or
the adapter). I stuffed the adapter into the $C000 socket and was
reading the contents with a Fluke 9010A in the CPU socket. BASIC and
KERNEL and real CHRGEN ROMs reads fine with this technique; I even
have Fluke signatures to verify ROM contents (and have identified two
bad ROMs from my parts bin). The ROM/adapter board in the $C000
socket reads all zeros, but that's consistent with its behavior in its
"normal" CHRGEN ROM socket, so I'm unsurprised I can't read it.
This board came to me with the CHRGEN ROM already bad. It has never
been known to work while in the owners nor my possession. I was
hoping to get a known valid ROM image so I could burn a replacement
2716 or 2732 and use either the original adapter or one that Jim Brain
has recently built (which has already been tested to work with real
JEDEC-footprint CHRGEN ROMs).
I have a photo of a Japanese keyboard map. I think I can use this to
cobble up a faux 901447-12 or near equivalent, but it sure would be
nice to get the data from a real ROM rather than guess.
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