piclist 2000\05\30\103444a >
Thread: LCD driving trouble
face BY : Dwayne Reid email (remove spam text)

<x-flowed>At 10:44 AM 5/30/00 +0100, Andre wrote:
>Hi all !
>I«ve been working on a CPU used to control a high teperature high pressure
>chamber based on a 16C622A.
>It has a LCD display (16x1) been drived using nibbles instead of 8 bits
>words. Unfortunatly I have no more free I/O pins to use.
>The problem is as follow:
>1. When I first turn the CPU ON everything goes right. The LCD shows the
>message it was programed to show.
>2. If I turn the CPU OFF and not after one or two seconds back to ON again
>the LCD shows anything but the message it was programed to show.
>3. If I wait a little bit more (5 sec.) before turning the LCD back to ON
>again everything goes right.
>4. If I turn the CPU OFF and back to ON two times without wait all goes ok.
>I am sening the data without using the LCD R/W pin. The data is sent to
>the display and the program waits it to stabilize before sending the next
>4 bits.

My off the cuff suggestion is that you are not properly initing the
LCD.  According to specs, you must issue the 'switch to 8 bit mode' *3*
times before switching to switching to 4 bit mode.  Repeat: you have to
issue the 'function set' command with the 8 bit mode bit set for a total of
THREE times before changing to 4 bit mode.

You would do this in your PIC init routines after each power up
reset.  Give it a try!


Dwayne Reid   <.....dwaynerspam_OUTspamRemoveMEplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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