I will try this also, but I inspired in my LCD routines from Bob Blick
and I guess he is more experimented than me and he hadn't had this sort
of problem. The most probable cause are the pull-down resistors tied
with the internal LCD pull-ups. After that, I will try to change the
delay from the interrupt locally to the LCd routine and disable the
interrupts while displaying something.
Thank you for your suggestion !

Lucian
-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Sergio Masci
Sent: 13 mai 2004 15:05
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC:] LCD Sometimes Displaying Unwanted Characters

Lucian,
Can you disable interrupts at the start of your fucntions (lcd_putcmd
and
lcd_putch) and re-enable them at the end. This would help you determin
if your
problem is interrupt related.

I guess from your delay
>         delaycount = T_120_US;  // asteapta 120 us
>         while(delaycount);

that you are using the interrupt handler to decrement "delaycount", try
changing
this to a local int and delay by counting down

e.g.
        int    my_delay;
        my_delay = 640;
        while(--my_delay);

Is it possible that your "delaycount" is being cleared or set somewhere
else in
your interrupt handler and killing your original delay?


Regards
Sergio Masci

http://www.xcprod.com/titan/XCSB - optimising PIC compiler


----- Original Message -----
From: Lucian <luciffer@HOME.RO>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, May 12, 2004 9:31 PM
Subject: Re: [PIC:] LCD Sometimes Displaying Unwanted Characters


> The procedures for writing a character and a command are as follows:
>
> void lcd_putcmd(unsigned char c) {
>
>         LCD_RS = 0;
>
>         PORTB &= 0x0F;
>         PORTB |= c & 0xF0;
>         LCD_STROBE;                             // se activeaza datele
>         PORTB &= 0x0F;
>         PORTB |= c << 4;
>         LCD_STROBE;                             // se activeaza datele
>
>         BKLIGHT = 0;
>         if (blight_on)
>                 BKLIGHT = 1;
>
>         delaycount = T_120_US;  // asteapta 120 us
>         while(delaycount);
> }
> void lcd_putch(unsigned char c) {
>
>         LCD_RS = 1;
>
>         PORTB &= 0x0F;
>         PORTB |= c & 0xF0;
>         LCD_STROBE;                             // se activeaza datele
>         PORTB &= 0x0F;
>         PORTB |= c << 4;
>         LCD_STROBE;                             // se activeaza datele
>
>         BKLIGHT = 0;
>         if (blight_on)
>                 BKLIGHT = 1;
>
>         delaycount = T_120_US;  // asteapta 120 us
>         while(delaycount);
> }
>
> I am not changing the direction of the PORTB pins and LCD_RS is RB0.
>
> Lucian
>

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