On 25/11/2009 02:04, Jonathan Gevaryahu wrote:
[ stuff which was below a signature line so it didn't come out ]
The ROM image came from from someone I've got data from before, who
fixes things, and says he dumped it from one he desoldered from a
working VT. I have no reason to doubt him.
The idea that DEC made a practice of arranging the checksum to come to
zero or end "00" is news to me. I'm fairly sure that's not the case.
There must be many exceptions, if only because there's often not a spare
location to store the necessary constant to adjust the checksum.
Having worked with DEC stuff when it was current, even though it was a
long time ago, I'm quite familiar with the ROMS, including in particular
Q-Bus devices and VT1xx devices, because I used to repair them, to
component level, for a living. In fact that's why I started collecting
the images.
Using different polarity chip selects on masked ROMs is common practice.
Many manufacturers did that, and it's not hard to get round. If your
programmer can't deal with it, just bend the pin carefully and use a
test lead to tie it high or low.
--
Pete Peter Turnbull
Network Manager
University of York