Trouble with bouncing DO-403 output when switched.

[johndstein]

I'm currently trying to communicate with an AND671GST display using a cFP DO-403 module. The display uses a falling-edge enable bit for the write latch. When I try writing to the display, I sometimes get double characters. For instance, when I write "abcdefg", I might get "abbcdeeffg". I think that my enable pin is bouncing when sent low, causing a double-write effect. I've simplified the code to a brute-force method, to eliminate software complications.

My question is this. Is there a way to improve the output of the module using software, such as a debouncing filter? Or should I just try solving the issue using hardware (capacitor). Any input is appreciated.

John

[Aaron_G]

The [c]FP-DO-403 module does not have any programmable filter settings. If you need to debounce the circuitry then you will need to add an external capacitor. Before you do that however, you may wish to check the signal with an oscilliscope to make sure that the problem is actually bouncing before wiring external circuitry.

Regards,
Aaron

[johndstein]

Thanks for the input. I have been able to hook an oscilliscope to the enable pin, but cannot detect any bouncing occuring in the output. I've also tried running the same code with a PXI-6508 digital IO module, and the display works perfectly.

In fact, I've tried runnin with PXI hardware at much faster speeds, and everything works wonderfully. But if I try cFP at those speeds, it won't even initialize. I'm definitely running out of ideas. Any further help would be greatly appreciated.

By the way, the DO-403 is set where logical true = GND and logical false = 5V (Vsup). Thanks again.

John