Category Archives: RetroChallenge

Getting started

Posted on January 1, 2012 by Eric

I’ve taken the covers off the Sol-20s and cleaned them up a bit, though a more thorough cleaning should be done. I’ve powered up one machine, and it mostly seems to work. As expected, all of the keyboards have a … Continue reading →

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Retrochallenge 2012WW

Posted on December 31, 2011 by Eric

I’m looking forward to starting on my Retrochallenge 2012WW project. Some of my tasks are: dig out a few Sol-20s see if any work replace keyboard foam pads. connect cassette interface to audio ports of Linux system save a block … Continue reading →

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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 →

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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 →

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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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Hacking HP-41 microcode

Posted on July 23, 2011 by Eric

Since I’m basically done with my original project, the rewrite of the Apple 1 monitor for the MC6800, I’m now spending my copious free time working on HP-41 stuff. I’m trying to hack together an expansion ROM that will support … Continue reading →

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