HP97 The journey begins
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10-19-2019, 07:31 AM
(This post was last modified: 10-19-2019 07:35 AM by teenix.)
Post: #137
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RE: HP97 The journey begins
Hi all,
Another fun filled day. The next morning when I got up after my excited card reader working announcement, the bubble burst as it would not read anymore. Data was coming out of the reader chip ok, so I wrote a small piece of code to mirror the RA/RB data onto 2 spare output pins of the processor so I could see that the PIC was actually seeing the data. It showed that the PIC was missing some of the data transitions and cause a checksum error. Fast forward 10 or so hours and still I could not figure it out. I rehashed the code over and over to try and see if that was the problem, but no go. I built a new CPU board and same problem. Just as I was about to concede defeat (again), I looked at the pins connecting the card reader to the CPU board. With the normal CPU board plugged in, the reader circuit board can only be pushed in until it touches one of the ROM chips. With my board, it can be pushed in a little further. The connector pins taper down and pushing them into the mating holes further means the pin to hole tension reduces and the RA pin must have "just" been connecting. I put the board in it's normal position and it was happy again. Some of the things you learn the hard way :-) I hooked up the Bluetooth and mated it with my PC and I now have wireless connection to the HP-67 to transfer data which means you don't have to open the case. There are a few minor quirks with this but a software tweak will fix. I loaded the card auto read test program from the HP-67 user manual page 295 and the card auto loaded on PAUSE. This also worked when the calculator was instructed to get the program from memory storage. W/DATA also works manually and from a program. I tested the card write protect override option and when enabled, you can now easily re-write cards that were write protected. This means you can read cards and store the program on the PC or in the memory chip, which holds about 900 programs, and then if your original card fails, you can re-write it with the original code. The completed CPU board is shown in situ below. cheers Tony |
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