Category Archives: Calculators

More progress to report, after all

Posted on July 31, 2011 by Eric

I fixed several bugs in my code, and now the DIY4 can display the directory of an SD card and read and write files. It’s not perfect, as the first I/O fails, but subsequent accesses succeed. I’m using the open … Continue reading →

Posted in Calculators, Hardware, RetroChallenge, Software | Leave a comment

Declaring success

Posted on July 31, 2011 by Eric

I completed my original RetroChallenge project, the rewrite of the Apple 1 monitor for the MC6800 microprocessor, sooner than expected, so I’ve spent my spare time for the rest of the month working on HP-41 calculator stuff. I analyzed bugs … Continue reading →

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Display contrast in DIY4

Posted on July 26, 2011 by Eric

The DIYRPN 4 calculator uses a 16×2 character LCD module. The choice of module was limited due to the desired physical width of the calculator. We chose a module made by Lumex. The module is specified for operation on a … Continue reading →

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Keyboard scanning on the DIY4

Posted on July 25, 2011 by Eric

I tracked down a bug in the keyboard scanning of the DIY4 today. I thought there needed to be a delay in the scan routine between writing the scan lines and reading the return lines, but it turns out that … Continue reading →

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Bit-banging FRAM on the DIYRPN 4

Posted on July 25, 2011 by Eric

I’ve written code that successfully reads the vendor/device ID and serial number from a Ramtron FM25VN10 SPI FRAM chip. I haven’t yet read or written data. The code is currently using GPIO bit-banging, but the hardware is designed to allow … Continue reading →

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HP-41 card reader bug

Posted on July 25, 2011 by Eric

It occurred to me while studying simulator traces that it might be interesting to investigate a bug in early versions of the 82104A card reader for the HP-41C calculator. The bug was fairly esoteric and easily avoided, as it seemed … Continue reading →

Posted in Calculators, Nonpareil, RetroChallenge | 2 Comments

HP-41CV ROM set version HFF bug fix

Posted on July 25, 2011 by Eric

As I was studying HP-41CV microcode running in simulation, I finally uncovered what one of the bug fixes in the HFF ROM version does. This has been a mystery for many years, though there’s still one more unexplained change relative … Continue reading →

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Nonpareil status

Posted on June 11, 2008 by Eric

I’m still making progress towards a new release on Nonpareil.  Sometimes it seems like the more work I do, the more I find that needs to be done.

Posted in Calculators, Nonpareil | 8 Comments

R.I.P. Henry Horn, 8 August 2007

Posted on August 17, 2007 by Eric

Henry Horn was the editor of HP Key Notes.  He was very well known in the HP calculator user community, and will be missed.

Posted in Calculators, In memoriam | Leave a comment

Finally, a new HP RPN calculator!

Posted on May 28, 2007 by Eric

It appears that a retailer has spilled the beans on a soon-to-be-introduced HP 35s calculator. HP had said to expect a new model to commemorate the 35th anniversary of the introduction of the HP-35, the world’s first handheld scientific calculator. … Continue reading →

Posted in Calculators | 8 Comments