Open drain pin configured as input

[Murugesh_89]

Hi,
In pic microcontroller RA4 is the open drain output pin. I know that if this pin is configured as output we need to pull up with a resistor to drive. Pull down this pin will not work to drive high value.

If we configure this pin as input will this pin capable of detecting both high and low value?
I mean that i want to know, shall we pull down this pin to detect the high value and pull up this pin to detect low value.

Or this pin should be pulled up only on configuring this as either input or output?

Thanks,
Murugesh

 

[wp100]

Hi,

If you look at the chips data sheet Ports and RA4s diagram you can see that its Output only has the single N transistor were all the others have a P and N transistor.

The Input circuitry is unaffected by the output circuit.

Inputs, including RA4, generally need to have a weakish up or down resistor, typically around 10k as leaving them open circuit is not good.
Your input devices output signal is normally strong enough to ignore any input pull up or down resistor, so its only the default logic of the resistor that matters to your programming. That is a pull up will produce a 1 and pull down will produce a 0 if the input device is disconnected.

Be aware that RA4s input is a Schmitt Trigger type which mean very specific high or low levels must be attained to cause it to toggle from H to L or L to H.
See Wiki for details.