Re: HP41 bus analyzer Message #12 Posted by Eric Smith on 22 Feb 2004, 1:53 p.m., in response to message #11 by Michael F. Coyle
Thanks for the offer! However, I'm mostly looking for spares that I can actually completely disassemble (desolder chips from PCB), so I wouldn't want to do that on a calculator that was just on loan.
I haven't found my HP-25 yet. If it's not working (like two out of three of my HP-21s), I might want to borrow one, though I wouldn't desolder anything.
The purpose of desoldering chips is to run the ACT and the bank-switched ROMs in isolation in test circuits, in order to reverse-engineer the instruction set and the bank switching more easily. A PIC microcontroller will be wired to the bus for stimulus and capture. I suppose I'll do that with the ACT on my working HP-21, though I would have preferred to do it on a spare. It's possible that some ACT chips in later models such as the HP-19C/29C/67/97 may have added features, so if I can't get the microcode from all the calculators running correctly in simulation, I may have to do these experiments again with a later ACT.
It's possible that some or all of the chips in my non-working HP-21s might be OK, but I have limited time to spend on this so I'd prefer not to waste a bunch of time on chips that might be bad.
The HP-25 doesn't use bank-switch ROM. I'm fairly sure that the only second and third generation calcs that use bank switching are the HP19C, HP-67, HP-92, HP-95C, HP-97, HP-34C, and HP-38E/C. I only need to desolder the ROM from one second generation and one third generation calc. I'll probably do that with my HP-97, and take Nelson up on his offer of a set of chips from an HP-38C.
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