I need to know the threshold for high voltage 1 and low voltage 0 for a PIC. Which chapter in the datasheet would tell me this info usually?

 

Should be in Electrical Characteristics.
The table headings are "Input High Voltage" and "Input Low Voltage" in the datasheet I'm looking at (16F819).
If your datasheet doesn't have them, then see if a similar PIC does. You should be aiming to exceed the values anyway.

 

You need to tell us which PIC you are using.

 

Im using the 12f1822

 

Inside the "ELECTRICAL SPECIFICATIONS" area you will find "Input Low Voltage" and "Input High Voltage" tables.

The voltage varies depending on which pin, which pin function, and the supply voltage you being used.

 

Page 352 shows VIH and VIL.

 

And you need to check in the chapter on "PORTS" to see if those input pins are TTL or ST type, it can vary from pin to pin.

Also the specs in the electrical characteristics for the ST specs are not very correct, they usually state 0.2Vdd for low, and 0.8Vdd for high (1v=low, 4v=high) but those are "worst case" and when you actually test the PIC ST inputs they are more like 1.2v=low and 3.3v= high.

So the best answer is probably to test the pins.

You can do that with a pot on the input pin, and program the PIC to echo the pin state on an output pin.

Or you can connect an RC from an output pin to the ST input, and program the PIC to echo the pin but inverted, that will oscillate between the LO and HI levels and you can see the levels on a 'scope.