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HP 35 ROM fault?
11-22-2016, 02:20 AM
Post: #3
RE: HP 35 ROM fault?
(11-21-2016 10:52 PM)Harald Wrote:  ... Would anybody know which instructions are only use by those four functions and which of the three ROMs that would reside in?


One of my HP-25 calculated wrong sin, cos and tan results. As it turned out it was a single bit ROM error.

Recently I read the classic ROM code from an HP-70 by interrupting one single PCB path and attaching four wires to a PIC working as a address scanner. You could read the ROM code of your HP-35 and compare it with the original.

More interesting question is how to repair the ROM chips. An idea could be to add a tiny processor, which listens to the addresses and corrects the false bit by pulling down the serial data line at the right moment. Smile


That's one small step for a man - one giant leap for mankind.
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Messages In This Thread
HP 35 ROM fault? - Harald - 11-21-2016, 10:52 PM
RE: HP 35 ROM fault? - teenix - 11-22-2016, 12:20 AM
RE: HP 35 ROM fault? - PANAMATIK - 11-22-2016 02:20 AM

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