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arbitrary text messages
Monday, February 17 2003
I awoke a little after 6am this morning and resumed work on my cash register display interfacing circuit. The key to placing the display in a known part of the computer's I/O space proved to be in the jumpers for the other functions of the multifunction board. One of these jumpers switched the location of the board's parallel port from $378 to $278. I simply ran the display's chip enable line to the pin that wasn't connected by the jumper, and that had the effect of placing the display in the place where the parallel port wasn't. This was how my display ended up at I/O location $278. Not knowing the software protocols for communicating with the display, I just experimented until I figured it out. By putting a value between 0 and 31 in $279, I could move the cursor to that absolute location. Values in the range of $47 to $4B changed the display's brightness. By putting an ASCII value in $278, that character (or its control effect) appeared on the screen and the cursor advanced one position. Once I managed to track down a copy of QBASIC, it wasn't hard to write a little program to put simple messages on the display. It's difficult to describe the satisfaction one feels when one successfully displays arbitrary text messages on an old trash-picked cash register display.
In other news, a huge winter storm dumped a couple feet of snow on the area throughout the day. In desperation, we finally caved in and called someone to plow out our driveway. In the evening, after an unexpectedly satisfying conclusion for Joe Millionaire (yes, I realize we were manipulated to feel this way), Gretchen and I went for a walk in the blizzard. There was enough light from the full moon making it through the diffusing layers of clouds to light our way shadowlessly. Once a photon elbowed its way through the clouds, it ricocheted zillions of times off of all the reflective surfaces before crashing catastrophically into something dark such as a pine needle or a scarf.
How I interfaced the cash register display to an ISA PC multifunction card.
I soldered most of the wires to data pins exposed on a 74LS245.
The display working with some data from the Windows 98 master (the disembodied circuits above it).
This message suggests an application: on-the-fly bumperstickers.
The floor of the laboratory from a low angle.
The disco ball assembly under the peaked ceiling of the laboratory.
Click for a wider angle.
Sally in the laboratory.
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