Is possible do this logic?

[BotBoy]

Hi...

An input can be the level 1 if is powered level 0 if is grounded.
Most the time I always do this logic of the input using 1 or 0.

Is possible have a 3rd input state?

Suppose I need only grounding some input pin (level 0) ,
how is possible verify when the pin not is grounded if never i will have a level 1
on this pin.

is possible do this logic?

if PIN is grounding
do something

if PIN not is grounding and dont have high level as input
do something

regards

lucasi

[jbmiller]

There are at least two ways to accomplish this.
First, easy, use an ADC or Comparator input pin.
Second, a little harder, is to sample the Input pin to check for the 'high-float' condition, 'tristate'...which is a trademark btw)
If you use Google, there will be tons of applications of this 'old school' technique to get more information with less pins.

hth
Jay

[dezso]

Yes.
I have done similar to check if the remote switch is connected or not.
Turn on the PWM if you pic has one, or just create a 1KHz osc from a 555,
feed the PWM or ext_osc output on a 1K resistor back to your input pin, probe your pin for 500ms to see if you have a pulsing cycles or steady low or high.
There is your 3 state.
1:low
2:high
3:pulsing

[languer]

To clarify, you want to determine if:

• Pin is high,
  
• Pin is low,
  
• Or Pin is neither high or low - it's tri-stated (or not connected)

If this is the case look at Microchip's Tips'n Tricks 8-pin FLASH PIC Microcontrollers. In particular you're looking for TIP #3 Read Three States From One Pin.

If all you want to do is determine if:

• Pin is low,
  
• Or Pin is neither high or low - it's tri-stated (or not connected)

Then weakly pull-up the pin and test for HIGH or LOW.

[BotBoy]