repairing early HP calcs
ard at p850ug1.demon.co.uk
Mon Dec 19 18:07:19 CST 2005
> I dont own any. But according to a recent Circuit
> Cellar article, early ics can be easy to implement in
> a FPGA. Dont have the issue in front of me, but the
> guy needed to mimic if you will a crt controller.
> Therefore could the chips used in the early HPs (maybe
> up to and including the 41 series?) be readily
> emulated by an FPGA?
There are 2 main problems...
1) The triival one is that the HP calculators did not use standard logic
levels. The Classics, Topcats and most of the Woodstocks (HP27 being the
exception) are PMOS, for example
2) The more serious problem is lack of documentation for the ICs. Eric
Smith knows more about this than me, having written emulators for these
machines, but in many cases data sheets plain don't exist, and when they
do, there are odd quirks. The NUT processor in the HP41 has a number of
bugs compared to the data sheet I have, for example.
And of coruse fitting an FPGA in place of an HP ROM/RAM chip (which would
cotnain, perhpas, 1K words of ROM and 16 56-bit 'registers' of RAM, with
an odd internface to the rest of the machine) which comes in an 8 pin DIL
package is another entertainment.
So yes, it can be done, but it is not trivial.
Shameless Plug Alert!
If you want to repair HP calculators, consider buying the HPCC Scheamtics
CD-ROM. It contains scehmatics for almost 70 calculators, small
computers, peripherals, etc. No, I don't get anything from the sales,
other than supporting HPCC.
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