Palm Pilot LCD screen pinout in progress

[pproc]

OK, after some experimentation I am reasonably sure of the following on my palm pda type lcd (Picvue PC1721WE).
I'm not sure if it is for a genuine Palm PDA as the icons on the 4 corners of the "graffiti" interface pad are different from the original Palm PDA panel.

1. Its a 4bit monochrome panel
2. Has onboard EL driver using HV826 driver chip
3. Has onboard contrast voltage generation circuit

Pinout

20 D3
19 D2
18 D1
17 D0
16
15 CONTRAST (pwm ? 0 =>15V, 3.3V => 21.5V)
14 DISP_EN
13 GND
12
11
10
9 HSYNC (LP)
8 DCLK (CP)
7 GND
6
5 BKLIGHT_EN
4
3 touchscreen
2 touchscreen
1 touchscreen
0 touchscreen

I'm not sure of the VCC pin on this pinout because it doesn't seem to be directly connected to other chips on the
board or to the display lines. So I am powering
the panel by connecting 3.3V to the HV826 driver VCC pin.

I'm pretty sure of the DISP_EN, HSYNC, DCLK and D0 .. D3 lines, because I can bring up the screen for one frame with contrasty lines, placed where I would expect them e.g. Writing 0x8 every data clock to D3..D0 makes the 1st,5th,9th pixels on a line black. Writing 0x1 makes the 4th,8th,12th pixels black..

For these experiments I have been using Daltore's experimental data, driving the pixels with an approximate pixel clock period of 75uS.

However, the screen fades immediately after the first frame draw. So I have not yet been able to determine the VSYNC (FLM) pin (and perhaps a BIAS signal, though I don't see it on the PC0919WE07 schematic) and timing.

Again, any pointers to useful info would be appreciated - i am close, but not yet there !! Am wary of doing damage as I only have a couple of these screens and could really make use of them.

[daltore]

Hey, I'm glad to see you're getting results! I have had absolutely no time to work on this, and I've gotten side tracked into different projects when I do have time, but I do intend to eventually work on this, if for nothing else than hacker points. Keep us updated on any progress you make, and good work!

[audiocanine]

I was wondering how you are figuring out what all the pins do? What equipment are you using and what are you doing with it? And furthermore, how would I go about testing the function of electronic components (especially LCD displays) in the future?

Thanks

[pproc]

Well, a multimeter to check continuity told me which pins were ground. Since there was an EL backlight driver chip with identifiable part markings, the datasheet told me which pin was VDD and which pin was the backlight enable.

The digitizer pins were easily traceable to the touchscreen.

There were 4 pins going to adjacent 4 traces close to the lcd glass, so guessed (correctly) they were the databus.

There was some circuitry and a test pin on the PCB that showed a high voltage (> 15V) so I figured the LCD contrast voltage was being generated onboard. One of the interface pins affected the voltage - setting it to 0 made the voltage 15V and setting it to 3.3V made it around 19V. So I guessed it was PWM control for the contrast.

Then, used a PIC32MX breakout board and soldered gpio pins and started experimenting, using the olimex code as a starting template.

The display enable pin was easy enough to find, not even an lcd flash happening until a particular pin was logic high.

Setting individual bits on the data bus told me the high-low order.

That left the timing signals and some possibly unknown control voltages.

Experimenting, I got as far as a very dim and flickering screen with my text in the right place. Pretty much unusable - something incorrect with the timing signals and/or driving voltages and I shelved the project last year.

And I am not sure if I damaged the lcd during the process or if the lcd was defective to start with. The EL backlight driver doesn't seem to be generating the minimum 80V ac required voltage, i can only see about 40V at the output - this is on both the units I bought.

[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.