From the mail list..
I'd love to take one of the LCDs home at the next meeting. Would I need "the big card" as well to get them running via your instructions? I'm hoping to just follow what you wrote exactly and see if I can get one displaying something for myself.
Yes, the display needs to be driven by the MSM6255 chip and its related circuitry, which is on the big card. The other stuff is a RAM chip, which holds the currently displayed image (the "frame buffer"), which is continuously read by the MSM6255. There's also a '245 buffer chip, with lets you override the MSM6255's control of the RAM, so you can write new image data into it. The display runs on +5 volts, as does the card. The display also needs a negative supply, which is produced from the +5 by the circuitry on the far edge of the card.
The motherboard has what looks like the same circuits on it, used to drive the other display. I haven't traced out of the signals on the motherboard like I did on the card, but if people use up the cards and can't figure out where to tap the signals on the motherboard, I could do it.
To use the display, you need to connect 8 data lines, 15 address lines, and 3 control signals (and short a couple signals to ground - and of course remove all unnecessary chips). Because the MEGA88 has so few I/O pins, I used three 74HC164 shift register chips connected to MOSI and SCLK to get all the address and data lines. If you used a chip like the MEGA644P with lots of I/O pins, you could probably just use I/O pins and not worry about the shift registers. Then again, there are never enough I/O pins so using only MOSI and SCLK is nice, even if it takes a little time to wait for the 3 bytes to shift out.
The 15 address and 8 data lines are all available at the socket for the EPROM or the right-most RAM chip (the one not used by the MSM6255). I built my board to just plug into the RAM chip socket to connect those 23 lines and also get power. That left only 3 wires to run to the rest of the board.
To write into the frame buffer is really very simple. You just output the 8 bit data you want, and the 15 bit address where you want it written. Then you drive the '245 enable line low to take control of the RAM chip, and then drive the write strobe low to write the data. Then rise the write line back high to complete the write, and the enable signal back high again to allow the MSM6255 to keep using the RAM normally. The buffer enable signal also connects to the DIEN pin on the MSM6255, so your 15 address lines get fed though the MSM6255 to the RAM while the buffer feeds your data to it. It's nice that they made both of them high for normal display operation and low for access to the RAM. There's also one other write strobe, which you use (without the buffer enable) to write configuration into the MSM6255 (see the MSM6255 datasheet for details, and my code for the config guesswork I did that seems to work pretty well - though other configs might be possible).
The one other thing you need to do is control the LCD negative voltage. There is a digitally controlled pot on the board. I just cut if off and wired in a normal pot, which was a lot easier for reverse engineering the display (while trying to guess the MSM6255 config settings, turning the pot back and forth and viewing from different angles could let me guess if parts of the LCD were being double-scanned from incorrect config - and believe me, I tried many incorrect settings!) If you want software control of the contrast, you might try configuring the pot? That should be pretty easy to troubleshoot since you can just measure the voltage as you try it. If you're going to replace with a normal pot, you'll need a 10K linear taper (maybe on the group order?)
I didn't draw a nice schematic (and don't plan to - but all the source code is online).... but maybe someone will draw something up to help others?