Ummm... Have pull-down resistors on data lines, Register select, and enable
line?
I got bitten by this a few times. If the MCU sleeps or resets, the pins
float, and may shift in spurious data.

- Robert

>-----Original Message-----
>From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]
>On Behalf Of Lucian


>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
>

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