Thank you very much for all answer and idea ! Here is more informations :

The uC is used to pilot a reveiver with PLL.
If the knob is turned slowly the frequency is incremented by 10kHz ; if it’s turned faster the frequence is incremented from 500kHz (for example).

To limit RF noise I like to put the 89C52 in Idle mode (Not yet implemented in the program). Also for wake up I need use interrupt. Also there isn’t polling.

The rotary knob is a ELMA (http://www.elma.ch/English/R...ames.html).
This knob is mechanical. 30 " click " for one turn.

For me I think it’s a bad choice because
- he give bounce
- the biggest problem when the output give 11 after the next click you have 00 ; no problem. But, the next click you have 11 and the INT0 can’t start ; the INT start only when the level go from high to low ! Also the increment is by 1 only after 2 click !


For the PETER idea:
I think the line :
Static char old =4
is at the wrong place. Because never the if or else is true ! (have you a C++ compiler ? my C51(Keil V3.07) doesn’t support the comment with //)

The idea to get 4 phases for one step is very good with a knob WITHOUT click. I you turn the button you have a click and you want to see the increment. It’s not natural to have click, click, click, click for 1 step.


I want to found and try an opto knob and give you more info. But not before tomorrow.


THANK ‘S again

Sylvain