Wednesday, October 19. 2016Rescuing data from an Epson HX-20 to a Linux PC
I recently managed to reactivate my dear old Epson HX-20, a retro computer released in 1983 which I used at the end of the 1980’s and early 1990’s to learn programming. Since I even could read in some BASIC programs that were still stored on the micro cassette, I wondered if I could rescue the code directly, without using OCR on printouts or even typing it off by hand. I was aware that I was very lucky that this machine still worked after all those years—the soldering seemed to have been much more rigid back then, it might cause more issues to attempt to run old PCs which are a decade younger! To be on the safe side, I invested into a new NiCd battery pack and replaced the original one. My research first led me to the machine’s RS-232 output, internally called “COM0”. Someone had used that some years ago to directly connect an HX-20 to a PC’s serial port, using a special cable and some adapters. Sadly, it seems that this is no longer an option, since these cables disappear, and serial-to-USB adapters only seem to work with a certain chip in this case. Then I stumbled upon the GPL software HXTape, and I was totally baffled: What, the Epson HX-20 had an external cassette interface as well? I knew that concept from our even older machine, the Texas Instruments TI-99/4A. It connected to a special music cassette recorder and encoded data into simple “magnetic bits” onto the tape: It was quite funny to listen to the noisy sounds when playing the MCs on an ordinary player. This bidirectional data transfer works over ordinary mono audio cables, one for each direction. And now, it turns out the HX-20 had such an interface as well, and we never used it. But the point is, one could exploit it to decode the audio signals into the original bits and bytes by connecting the HX-20’s “MIC” port to the microphone input of a PC using a simple mono audio cable with standard 3.5 mm jacks! (How tremendous the analog world was! Keep a music cassette lying around in the basement for decades and then just play it. Try this with your ¡Phone!) And that audio decoding is exactly what HXTape is doing. So, to test this interface, I connected speakers to the HX-20’s “MIC” port, wrote a “Hello World!” BASIC program, issued SAVE “CAS1:TEST”
on the HX-20, and—lo and behold!—I could hear those “noisy sounds” again after decades! My next step was to try to plug an ordinary external microphone into my (shiny new) Lenovo ThinkPad P50 which only has one of those 4-pole microphone/headphones combo jacks. I had purchased a Y-splitter cable to be able to use the mono input. After more than one hour I gave up: It’s simply not possible to use a microphone that way. A USB soundcard would have worked, but our 12-year-old notebook jumped to the rescue, which still had a standalone microphone input. HXTape is written in PHP, but you cannot simply run it on Windows, as it uses GNU/Linux’s Open Sound System (OSS). And herein lies the next stumbling block: OSS has been abandoned from modern Linux distributions some years ago (in favor of ALSA), and HXTape’s expected interface Finally, emulating the sound device and having the PHP scripts running, I attempted my first data transfer, but the script failed terribly by randomly repeating messages like “Start tape!”, “Volume too high!”, “Volume too low!” in arbitrary order several times. The solution was to simply
Sadly, it won’t be possible for me to actually run some of those programs on the PC, unless there’s an emulator that knows how to handle specific commands like I could capture almost all of the micro cassette, but then the HX-20 started to crash more and more often, showing garbage on the screen even after a hard reset. In addition, the LCD contrast has become quite low due to fading components impeding its voltage supply. I’ll try once again, but I’m afraid even more retries are becoming pointless. Anyway, for me, that was a quite interesting visit to the digital past, and an exciting case of computer archaeology! Trackbacks
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Markus on :
Thanks for this article! I’m still trying to figure out how to get hxsave.php to work. I want to encode some BASIC games from http://www.geocities.ws/abcmcfarren/hx20/hx20.htm . I think I have to refresh my PHP knowledge a little bit
Geoff Barnard on :
I’ve managed (with a lot of help from original writer of HXtape), to get this process working under Windows, so I can now convert my HX progs into text, edit/print/etc, then convert back to WAV. Great help. Fiddly process, but manageable.
Geoff
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