Re: HP-97 Bug - Do you think they'll fix it? Message #4 Posted by Eric Smith on 10 July 2008, 5:05 p.m., in response to message #3 by Patrick Rendulic
I can easily imagine two different reasons why this bug might appear on some HP-97 units and not others.
There were two firmware changes made during HP-67/97 production. ROM 0 (stored in the ROM/Anode Driver chip) was revised to fix incompatibilities with some revisions of the ACT (processor) chip. The original chip in the HP-97 was p/n 1818-0225, and it was replaced by 1818-0267.
ROMs 1 and 2 were revised as a pair to correct mathematical errors. Both the HP-67 and HP-97 originally used p/n 1818-0228 and 1818-0226, which were replaced by p/n 1818-0550 and 1818-0551, respectively.
It is possible that one of these changes either fixed or introduced the bug. The ROM 0 change is the more likely candidate. However, most of the printing code is actually in ROMs 5 and 6 in the 97.
HP had two vendors for the "PICK" chip that controls the printer in the Topcat series and 19C, AMI and Mostek. There are known to be functional differences between the two, so this is another possibility.
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