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Getting an S128240D up and running

I'm trying to get a new board running with an S128240D. The interface I've chosen is 8-bit 8080. I've based everything off of the reference schematic and code (correcting for 8080 mode). I'm using an external supply to drive VLCD and have left out the booster capacitors. The display doesn't do anything visible at any stage of initialization. I watched the communication with a logic analyzer and the signals are being driven correctly. In an attempt to see if anything was working at all, I put in some code to do STREAD commands after each command to see if I could read the internal status. The interesting thing is that the display is responding - sort of. Basically, it's echoing back the last byte I've sent it. I double checked that I am really reading from the display and not reading the value I had written to the port register previously. I do the command sequence, then switch the port to input (at which point the data bus goes high). I set A0 low, then /XCS low. As soon as I drop the /RD line low, data appears on the bus, and it's always the last byte I had written to the display (be it command or data).

Other data points: There is no voltage at V1, V2, V3, V4 or V0in/out. VLCD is 18V (external supply). I wondered if the A0 line was not going low to indicate a command. It doesn't seem to be the case, though. I can measure the voltage at the pin and it does go low at the appropriate time. I even tore up a display to get an fpc cable so I could check that there is a connection between the CPU and the FPC connector itself.

Can anyone suggest some strategies on how I can test this further? I'm not really sure how to proceed on this. Thanks!


Guest's picture
October 7, 2011

Nevermind! I was sending things too quickly to the display. Slowed things down a bit, and things are starting to turn on