Lucian,

I have seen the problem myself when I started using an LCD to display the
time.
Basically, the ISR was doing too much. It updated the time registers and
then displyed the time on the LCD. In other parts of the programme, other
parts of the LCD were being written to with other data. If the ISR fired
when data was being written elsewhere, then the time would be written where
it was supposed to be, but on return, the other bit of the programme would
write data to the next character after the time, or perhaps somewhere
random, depending upon how far it had got with setting the cursor position.

I don't know if you have this sort of problem or not, but I fixed it by
setting a flag in the ISR to say that the time needed updating, and then
checking this in the other bit of the program to see if the time display
needed updating.

Hope this helps......Mike.

----- Original Message -----
From: "Lucian" <luciffer@HOME.RO>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, May 12, 2004 8:59 AM
Subject: [PIC:] LCD Sometimes Displaying Unwanted Characters


> Hello again with another question on a different topic...
>
> I have an LCD 2x16 module driven by a PIC16F648A in 4 bit mode. It
> initialises ok, displays normally, but sometimes it displays the
> characters at unwanted screen locations or displays unwanted characters.
> I had a clock with blinking ":" displayed, but sometimes the time was
> displayed at the first row instead of the second.
> I have a menu displayed but sometimes it displays unwanted characters
> instead of the correct ones, I observed that often with one character
> ahead, e.g. "MEMU" instead of "MENU".
> I searched all the web, but only found a post for PIC Basic (I am using
> Hi-Tech PIC C) that was saying that it might be the interrupt service
> routine which doesn't save all the context before jumping to the
> interrupt so that sometimes the LCD routines are interrupted and don't
> execute correctly. I cannot disable the interrupts in the LCD routines
> as I have some timers and serial communication.
> I am sure that you know more than me on this issue. Could you please
> help ?
>
> Lucian
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Ken Pergola
> Sent: 11 mai 2004 23:28
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC:] Microchip PICmicro videos
>
> This link was posted in the Microchip Forums and I thought it would be
> worth
> posted it here:
>
> http://techtrain.microchip.com/x14/
>
>
> You'll find some professional videos related to PICmicro topics.
>
> Beginner or advanced, these might be worth your time. I only looked at
> one
> so far, but what I saw was very nice and professional.
>
>
>
> PICmicro x14 Basic Training Modules
>
> The following modules are available to help you familiarize yourself
> with
> the PICmicro MCU. Each module is an animated movie with audio.
>
> There is no installation necessary. Simply download the zip file to your
> hard drive and unzip the files. Each course should be copied to a unique
> folder.
>
>
> PICmicro x14
> ------------
> Architecture               (12.8MB)
> Instruction Set            (12.6MB)
> Device Configuration       (4.0MB)
> Resets                     (4.5MB)
> Oscillator download        (2.9MB)
> Development Tools Overview (13.3MB)
>
>
>
> Best regards,
>
> Ken Pergola
>
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