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'[PIC] LCD driving trouble'
2000\05\30@095007 by Andre

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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.

Any comments or sugestions are welcome !!!

Andre
spam_OUTacollingTakeThisOuTspamzaz.com.br

2000\05\30@103444 by Dwayne Reid

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<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



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

Celebrating 16 years of Engineering Innovation (1984 - 2000)

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</x-flowed>

2000\05\30@120804 by Jilles Oldenbeuving

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Hi Andre!


You might want to check the supply voltage to the processor. With some
capacity in your system
supply voltage will not be immediatly 0 V when you switch of the supply.
Let's say the voltage will
be 2.0 V when you switch on the supply again, a brown - out will occur. i.e.
the processor is
plain not running due to the fact that the Vdd didn't reach 0 V... i've seen
this in a consumer product
(vacuum cleaner). When programming your device be sure to set brown-out
detect on (and maybe
adapt your program to this).


By waiting longer before switching on the supply you make sure that Vdd will
reach 0 V, and thus
a brown-out will not occur.....


Regards,

Jilles Oldenbeuving
jillesspamKILLspamrendo.dekooi.nl
-----Oorspronkelijk bericht-----
Van: Andre <.....acollingKILLspamspam.....ZAZ.COM.BR>
Aan: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Datum: dinsdag 30 mei 2000 15:53
Onderwerp: [PIC] LCD driving trouble


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.

Any comments or sugestions are welcome !!!

Andre
@spam@acollingKILLspamspamzaz.com.br

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