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35th birthday soldering adventure
Sunday, February 16 2003
Gretchen and Blonde Tonya baked me a sort of spice cake for my 35th birthday. Meanwhile I was making a major push on interfacing the trash-picked alphanumeric digital display to one of my computers. It was a Merit 2X16 parallel display bar and a Google search had turned up nothing. I'd used a multimeter to trace the wires from the display's controller chip (an Intel 8742) to its pin array interface, which I documented:
Merit 2 by 16 parallel display pinout
| pin | 8742 connection
| | 1 | test_1 (connect to +5v to avoid demo mode)
| | 2 | /chip_enable
| | 3 | /read
| | 4 | a0
| | 5 | /write
| | 6 | d0
| | 7 | d1
| | 8 | d2
| | 9 | d3
| | 10 | d4
| | 11 | d5
| | 12 | d6
| | 13 | d7
| | |
| | 14 |
| | 15 |
| | 16 |
| | 17 | +5v
| | 18 | gnd
| | 19 |
| | 20 |
| | 21 |
| | 22 |
| | 23 |
| | 24 |
| | 25 |
| | 26 | |
I whittled down a connector for a floppy disk ribbon cable and then, when I got it to fit in the narrow space available, I attached it. At the other end of this ribbon cable I soldered the individual wires to appropriate places on an ISA multifunction card, the kind that comes with a serial, parallel, IDE, and floppy interface. The main reason I used it instead of something I could have made by myself was to avoid having to build and test all the address decoding circuits. Since I had no documentation for this particular card, I then had to figure out where within the computer's I/O address space the two controller ports for the new digital display now lived.
By now I've certainly lost the casual reader, who could never imagine using a soldering iron to connect an old cash register display to a modern Pentium computer. But let me assure you that it's actually fairly easy as long as you understand the principles of digital electronics and can solder neatly. I hadn't done this sort of work since the summer of 1994, but it came back to me just like riding a bicycle. Just so you know where the experience for such work comes from, let me provide a bulleted history of my work with custom computer interfacing:
- 1985-1986: lavish modifications to a stock Commodore VIC-20, giving it 100K of memory, voice synthesis, and elaborate new video capabilities.
- Winter 1991: similar modifications to a Commodore 128, using many components pillaged from the now non-functioning VIC-20. The Commodore 128 died after only a month or two of modifications.
- Summer 1994: similar modifications to a Zenith PC-compatible (8088-based). This machine is still functional.
I've bemoaned the fact that it is no longer practical (or possible) to modify modern super-miniaturized digital computer hardware. But a project like this display interfacing draws on some great aspects of older digital electronics (particularly display size and brightness) and combines it with the known-territory of a Pentium computer using the one interface that can still be monkeyed with: the ISA. As long as a computer has an ISA interface, I can build a card or modify a card to interface with it, allowing me to get digital data to just about any digital equipment, old or new.
I didn't actually finish today's interfacing project. I put it all together and the computer booted up fine, but then I had a devil of a time finding the display's I/O space so I could begin writing the programs allowing me to control it.
In celebration of my birthday, Gretchen and I went to Armadillo, a southwest-style restaurant in the Rondout section of Kingston. It was a wonderful place, with a cozy atmosphere, armadillo statuary, great staff, and excellent food (though the cooks might want to look into investing in some hair nets). I ate so much that I had to stretch out in my chair and put my feet up in an unused chair. When I did this, our waitress playfully chastised me for my unrefined ways. So I told her that I was a "cowboy electrician." When I asked for a shot of Pepe Lopez tequila, she went and got me a shot of much more expensive stuff (and evidently didn't charge us for it - we'd told her it was my birthday).
For linking purposes this article's URL is:
http://asecular.com/blog.php?030216 feedback
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