Re: [uCsimm] touchscreen

From: Tom Walsh (
Date: Wed Mar 21 2001 - 15:58:09 EST

David Beckemeyer wrote:
> Has anyone actually got the circuit referenced in the FAQ to work
> in real life:

Yes, me, I designed it.

> It seems like this circuit uses +5V on the SPI lines instead of
> 3.3V. Is this okay?

Yes, the DragonBall is +5volt tolerant on it's i/o lines.

> And the *TOUCHED interrupt signal looks like it only signals the
> interrupt for the currently selected axis (per the AXIS signal),
> which seems to mean that it will only signal a touch when both
> axes change, which makes it seem like you'd have to poll the
> circuit anyway.

This never really worked as advertised, the problem is that the input to
the gate would not swing far enough to have it change state. Sorry to
have caused any inconvience, this design was a published doodle
(exploration) into interfacing to a touch panel. For more details see:

> Can anyone supply working reference code for this circuit?
> Does anyone have other uCsimm/uClinux EZ328 touchscreen hardware
> and/or software they'd be willing to share?
> Anybody have code for an ADS7843 (or similar)?

Yes, see: '', I am now using the
ADS7846 controller and it works rather well. I am also using Phillipe
Ney's touch panel driver, in the Lineo CVS as well as my own CVS, the
driver is called 'mc68328digi.*'. I am still having some issues with
noise pickup from the LCD electronics, but your milage may vary.



Tom Walsh - WN3L - Embedded Systems Consultant
'', ''
"Windows? No thanks, I have work to do..."
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