Parallel LCD weird characters

[A387]

Hi all,

Since yesterday I'm busy trying to fix a LCD display connected on a parallel port.

I've installed 'port95nt', the drivers to communicatie with the LPT1 port.
The display is a Powertip 1602-q without backlight.

In LCD Smartie I try to use the HD44780.dll with 2x16 screen.
When I use this input: 'Hallo' and 'Amsterdam', I see this on my display:

H'lln
@lrtdrd'l

As you can see the output is almost the same, but I am quite suprised by the weird characters.

Does anyone have a clue what might be wrong in my setup?

[mattcro]

How long is the cable between LPT port and LCD? With long cables (>1m or more) you may get corruption like this. Try increasing the timing multiplier setting in Smartie (and restart Smartie).

Also try different settings for the LPT port mode (SPP, EPP, ECP) in the BIOS. I think some people have reported one mode working better than others.

Make sure you have at least 1 ground wire connected between the LCD and the LPT port, even if you use the PC's PSU for LCD power.

[stan001]

I also hv a PowerTip 2x16 LCD module and found out the garbage character was bcos the refresh rate was set too fast.. at 60-70ms is just nice..

I only encounter this issue when displaying winamp spectrum graphs with 2 lines but not with single liner graphs or text display...

I changed to a different 2x16 LCD module and the garbage issue went away and I can even set the refresh & dll speed to as long as 12ms..

Is it b'cos the PowerTip LCD module are "slower" than others and cannot support higher speed input or something ????


I made a parallel port version but only wired 10 pins, 1-9 and pin 16... do I really need to hv a ground connected between the parallel port to the LCD module ??

[mattcro]

That's interesting that you have found a difference in speed between different display modules. It could be that some (like Powertip?) are slower that others...

It's a good idea to connect the LCD ground (0V) to the parallel port ground. If you use a separate power supply (not the PC's own supply) then you must connect LCD ground to PC ground.