Ok, the LCDs came in and I figured out all the system settings.
LCD datasheet here (if you can call it that):
http://www.qingyun-it.com/products/y...LCM3202401.pdf
SED1335 controller datasheet here:
http://www.compsys1.com/support/docs/sed1330.pdf
I am driving it with a PIC 16F877 at 20MHz. Every thing goes fine, I can reprogram it over and over and change the text at will. But if I power OFF and back ON again the LCD goes crazy. It's like a TV that loses vertical control, just a blur of lines going super fast. If I wait 7 seconds or more before powering back ON everything boots up normal.
This is the 1st type of LCD controller that's ever done that to me and this is the 4th type I've tried so far. Has anyone ever encountered a similar problem? I'm guestimating that this particular controller requires a short break between power OFF and ON for some technical reason, why? No idea but that's what it looks like.
The initialization routine in the PIC seems fine 'cause it works perfectly if I wait 7 seconds or more. I can pull-down /MCLR as often as I want, the PIC resets fine and the LCD displays properly.
My rookie solution would be to control the power-up of the LCD with the PIC instead of feeding it directly from the supply line. A 10 second 'warm-up' period with a flashing LED and probably a transistor to power the LCD. The LCD datasheet says 90-100mA, that's more than what a PIC pin can drive (25mA if I read the datasheet properly). I was thinking of having the VDD direct to the LCD logic, and placing a transistor on the Vss like so (just to confirm I have my head on straight):
Base: control pin on PIC via a resistor, not sure what size but I know I need one.
Collector: LCD logic
Emitter: VSS
Does that make sense?
Robert
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