Palm Pilot LCD screen pinout in progress

[pproc]

Here is the pinout for the PC1721WE type lcd, similar to a Palm Pilot pda,
160x160 resolution, monochrome, EL backlight, resistive touchscreen.

Pinout

20 D3
19 D2
18 D1
17 D0
16 BIAS
15 VO_EN
14 DISP_EN
13 GND
12 3.3V
11
10 FRAME
09 LINE
08 CLK
07 GND
06
05 BKLIGHT_EN
04 touchscreen
03 touchscreen
02 touchscreen
01 touchscreen

All signals are 3.3V level.

The BIAS logic level needs to be inverted every frame. The VO_EN signal needs to be 3.3V for a legible screen. Tried PWM control of VO_EN but no luck, it wants a DC signal. I have not yet tried a separate supply for VO_EN with a higher voltage.

This LCD uses an onboard LCD drive voltage (15V - 19V generation system centered around an LM324 opamp,
and an EL backlight drive circuit using an H826 IC. The backlight drive does not appear to be functional, which may explain why this LCD display was available for $5.

I was able to use both the Olimex template code and the code here
http://www.cafelogic.com/articles-2/...-with-a-pic32/


as starting templates to get a working display. The Cafelogic code indicated the possibility of a frame inversion bias signal being required for my lcd, unlike the olimex lcd, and that turned out to be true.

Coincidentally enough, like the CafeLogic project, I was also using a PIC32MX mcu to drive the signals. So it was pretty easy to port his code to my MCU derivative and LCD.

I checked out the CafeLogic code generated signals with a usb logic analyzer. Interesting - an interrupt service routine is called periodically for each line, the previous line data is latched in with the line pulse, and then the following line data is written as fast as the C code can run. Thats how he gets the 93% idle time with an 80Mhz cpu clock, and the display seems to be OK with accepting this timing.

Not completely usable yet - still some flickering and streaking on the image. The attached snapshot is with the Cafelogic derived code which prints out the % free cpu cycles, i.e. cycles not used by the lcd driver code on the PIC32MX.

This is happening with my olimex derived code as well, possibly there is a sweet spot in the timing, also my ratsnest wiring to the tiny lcd connector is likely not helping with the high speed clock signals.

Its also possible i damaged the lcd in the course of my experiments. Still, at least I am sure of the pin functions above, have not tried the touchscreen yet.