Re: Problem with PIC & LCD display

On Fri, 2 May 2008 17:47:32 +0100, Steve H <steveu@xxxxxxxxxxxxxxxx>
wrote:

In message
<2afa43ee-b6af-4408-8e36-93f87d537027@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, mpm
<mpmillard@xxxxxxx> writes
On May 1, 6:330 >
Hey. Read all the posts....
My experience with character LCD's (in general) is that they are
pretty forgiving and robust. Most folks have trouble getting them
going, especially in 4-bit mode, because they try to read the busy
flag before the device is fully initialized.

So, my advice is: double-check your timings, even though it seems to
"work" as you have it. Doesn't take that long. Start with the
basics...

Another possibility (not sure if already mentioned), check your solder
joints. Could be a bad joint.

Otherwise, yes, I'd have to agree you either have a bum display (have
you tried replacements?), OR there's some glitch on the power rails.

I'm a little curious what your R/S, R/W and E lines are at (or
supposed to be at?) when this problem manifests. If you're not
writing to the display, then trash on the inputs should not even
matter! That leaves only the strobe (again, should not matter in read
mode), and the power rails.

I'm also wondering if the backlight has anything to do with this? I
assume from your write-up that the display will go blank even if the
backlight is not instructed ON.?

One more thing you might try: Slow everything down in software.
Maybe the LCD is working correctly, and it's the PIC that's telling it
to clear in response to whatever it is that you're doing to cause the
problem to appear? In other words, not the display directly, but
indirectly via the PIC.

Insert a couple million NOP's in the strobe routine ought to tell you
that real quick.


The program is written in basic using the Proton+ compiler. Default LCD
timings have always worked before using this compiler, though they can
be altered - something I have tried with no success. This PIC + LCD
setup ran perfectly under test for several weeks on a breadboard layout
before the final unit was constructed.

I've also disabled and isolated the backlight supply, so can rule that
out as the cause.

Good luck.!!

Thanks!

-mpm

Given the results in this thread so far, the problem is someplace no
one has looked so far. Per the novels, after eliminating all other
causes, the remaining however implausible, must be the clue.
.

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