messed up lcd data lines

[tristantech]

I am interfacing a graphic LCD i bought at sparkfun with an Atmegat644. I know the code is fine, because this has worked a few times, but it fails 99% of the time. Anyways, to make sure the code was working, i probed some of the lines with a 'scope and saw this on the data lines. (see picture below)

I think this is the problem... The signal has these funny decays and all kinds of noise that is mis-interpreted by the display. This is on every data line, but not any control lines. data lines are on PORTB. The internall pullup resistors are off and the data lines are bi-directional

My Question is: why does this happen and how can i fix it?

[Soeren]

Hi,

[...] I know the code is fine, because this has worked a few times, but it fails 99% of the time.

"Fine" and "Fails 99% of the time" seems to me to be *ahemm* slightly conflicting terms.

Anyways, to make sure the code was working, i probed some of the lines with a 'scope and saw this on the data lines. (see picture below)

I think this is the problem... The signal has these funny decays and all kinds of noise that is mis-interpreted by the display. This is on every data line, but not any control lines.

If you're absolutely sure it's soldered perfectly, try slowing the comms down just a bit, to see if the errors diminish or vanish completely. What happens then?

Did you perhaps use long leads between the controller and the display?

Do you use the busy signal to pause comms, or do you just spurt it out as fast as possible?