LCD display glitches with interrupt

[Art]

Thanks Heckler, I have done something similar after Googling the problem,
but since the device is in a car, I can't test it every time I change something,
and tend to wait till I'm driving anyway.

The ISR has RB0 trigger as a possible source as well. I have tried this:

intsync = 0
LCDOUT $FE,2                                    'VFD cursor return home
FOR gcnt = 0 TO 39                                'print data to vfd
LCDOUT vfd[gcnt]                                '
NEXT gcnt                                        '
'
if intsync = 1 THEN                                '
intsync = 0                                        '
LCDOUT $FE,2                                    'VFD cursor return home
FOR gcnt = 0 TO 39                                'print data to vfd
LCDOUT vfd[gcnt]                                '
NEXT gcnt                                        '
endif                                            '
'
if intsync = 1 THEN                                '
LCDOUT $FE,2                                    'VFD cursor return home
FOR gcnt = 0 TO 39                                'print data to vfd
LCDOUT vfd[gcnt]                                '
NEXT gcnt                                        '
endif                                            '

40 char, single line display.
The ISR sets the status of intsync.
Fingers crossed

[Darrel Taylor]

LCDOUT is a "Synchronous" command. Meaning that data is clocked in only when it's known to be valid on the data buss.
It is not affected by interrupts at all.

LCDOUT's in the ISR could be problematic, but I doubt you have any in there.

You are using a long cable to the display right?

[Art]

Yes Darrel, but I've since tried some other things, and am almost ready to discount interrupts as the problem.

I now think it's to do with writing custom characters to the display, or more accurately altering custom characters.
This is happening frequently with both the timer, and a tachometer bargraph.
I might just have to give up the rolling odometer effect for the elapsed timer.

[fratello]

I have three "type" of LCD display ; all are HD44780 compatible, all are Made in P.R.C. .
Two of them "react" verry slow : it's impossible to use "scroll effect" and, sometimes, glitches...
One of them (top of picture, left) it's OK ! All the informations are displaying correct and without any glitches, no matter what.
I tested them using same hardware : 16F684 - without ussing interrupts !!!
Maybe the hardware inside of LCD's it's the problem !

[Art]

It does appear to be the LCD, it's a VFD actually, but with the same controller so LCDOUT commands are used.

I am able to confirm everything is fine if I do not update any custom characters, but can use them if they are defined
at the start of the program and then not changed, so no scroll effect

One interesting thing I learned is that if a custom character is being displayed, and then you change it,
the display does not need to be updated, the character changes instantly on the display.