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'[PIC]:LCD startup'
2002\09\27@100507 by Ryan Haley

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I am building a circuit that uses a PIC 16f84 to control and LCD screen.
Everything is well and good except upon startup, the LCD sometimes displays
only part of the default screen.  If I reset the power several times,
eventually I'll get the correct startup screen.  Any ideas on what I can do
to fix this would be appreciated.  Thanks.

Ryan Haley

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2002\09\27@111714 by Tim Webb

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What type of liquid crystal display controller/Driver are you using?

You might have to issue commands to the LCD Controller a little bit slower or at power on, wait up to 15ms after Vcc is 4.5V before talking to the LCD Controller.

Also check you signals under a load with an oscilloscope, you may need pull up resistors...

{Original Message removed}

2002\09\27@114012 by Ryan Haley

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It is an Optrex PWB 16129 Display with the standard Hitachi 44780 driver.  I
have a 60ms wait now to allow the LCD to power up, and 60ms between
commands.  I will check the signals with a scope.  Thanks!

Ryan

{Original Message removed}

2002\09\27@120457 by Wagner Lipnharski

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Ryan Haley wrote:
> I am building a circuit that uses a PIC 16f84 to control and LCD
> screen.
> Everything is well and good except upon startup, the LCD sometimes
> displays
> only part of the default screen.  If I reset the power several
times,
> eventually I'll get the correct startup screen.  Any ideas on what I
> can do
> to fix this would be appreciated.  Thanks.
>
> Ryan Haley


Hi Ryan, if this is an alphanumeric display, you should be aware that
if you are driving the LCD using 4 bits mode, remember that at
initialization the LCD expects 8 bits mode even that it only uses 4
bits. It can confuse the LCD if the RESET happens in middle of another
LCD commands.  One way to solve all those issues, is using a port pin
to drive power to the LCD, yes, the LCD consume is less than 1mA, so
most microcontrollers can supply that power to the LCD.  At your uC
Reset routine, just drop power to the LCD, wait at least 100ms, then
restablish power again, so, you will make sure that after each Reset
the LCD will restart fresh with a new initialization sequence.

/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Wagner Lipnharski - UST Research Inc
Orlando FLorida - USA - http://www.ustr.net
/_/_/_/ Atmel AVR Consultant /_/_/_/

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2002\09\28@150942 by akieran

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I had a similar problem at one point.  It went away when I
added decoupling capacitors between Vdd and Vss near the
processor, and near the LCD connector.

Andrew



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---- On    , Wagner Lipnharski (wagnerspamKILLspamUSTR.NET) wrote:

> Ryan Haley wrote:
> > I am building a circuit that uses a PIC 16f84 to control
and LCD
> > screen.
> > Everything is well and good except upon startup, the LCD
sometimes
> > displays
> > only part of the default screen.  If I reset the power
several
> times,
> > eventually I'll get the correct startup screen.  Any ideas
on what I
> > can do
> > to fix this would be appreciated.  Thanks.
> >
> > Ryan Haley
>
>
> Hi Ryan, if this is an alphanumeric display, you should be
aware that
> if you are driving the LCD using 4 bits mode, remember that at
> initialization the LCD expects 8 bits mode even that it only
uses 4
> bits. It can confuse the LCD if the RESET happens in middle
of another
> LCD commands.  One way to solve all those issues, is using a
port pin
> to drive power to the LCD, yes, the LCD consume is less than
1mA, so
> most microcontrollers can supply that power to the LCD.  At
your uC
> Reset routine, just drop power to the LCD, wait at least
100ms, then
> restablish power again, so, you will make sure that after
each Reset
> the LCD will restart fresh with a new initialization sequence.
>
> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> Wagner Lipnharski - UST Research Inc
> Orlando FLorida - USA - http://www.ustr.net
> /_/_/_/ Atmel AVR Consultant /_/_/_/
>
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> http://www.piclist.com#nomail Going offline? Don't AutoReply
us!
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>
>
>
>

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