Inconsistent output on a 4x4 matrix keypad

[markcadcam]

I'll give it a try.

Thanks,
Mark

[Ioannis]

If you still have problem after Steve's suggestions, please check the circuits. Better send the circuit here to see how you connected the buttons to the PIC. I suspect noise from some lines.

Ioannis

[mister_e]

FYI, using his code, i had similar problem as markcadam, so i decide to use my 'easy to use' INCLUDE with the same PIC and crystal... confirm that my hardware was good (EasyPIC4 + Keypad 4X4 adapter). Worked with internal pull-up AND external (of course).

Then i worked around his code. Use LATB intead of PORTB to write to the port for safety sake. On a whole port write, it doesn't really matter.. but when you write to few bit .. it may cause some problem. In this case leaving PORTB AS IS, will work anyways.

Writing to PORT before TRIS is also for safety sake even if some don't believe it But if you leave it like this... it still working.. but sometimes you have some screwed values

BUT the real magic is in the @ nop. remove those lines and the readings are screwed up.. or intermittent. just by this famous PIC18Xxxxx feature called 'Read/Modify/write' behaviour.

18Fs are much noise sensitive.. so i would avoid to use internal weak-pull-ups... IMHO.. you know i hate those anyways

[mister_e]

mmm, just double/triple/quad check the whole thing...
it appear that the TRIS work better if before the PORT/LATB line ....DOH!

BUT if you want to use the 'Microchip says' approach (write to PORT before TRIS), replace @ nop by @ GOTO $+2

That way... it works ... a treat

M.F.Sorry!

[Ioannis]

Hi Steve. Doesn't @ GOTO $+2 being equal to jump to next instruction? Also the same as NOP. So whats the difference?

Ioannis

[mister_e]

ASM GOTO need 2 cycle to execute, NOP only 1 cycle

[Ioannis]

Yeap. You are right. Its a typical delay then...

Ioannis