quick question 12F683

[HenrikOlsson]

Hi,
Looking at page 121 in the datasheet it says that when Vdd is between 2.0V and 4.5V a TTL input is considered high when the voltage on the pin is 0.25*Vdd+0.8V. With a 3.3V supply this equals 1.625V so 1.2V is not guaranteed to be interpreted as a logic 1. For a schmitt trigger input the number is 0.8Vdd which for 3.3V is 2.64V so even "worse" in your case.

/Henrik.

[peterdeco1]

Thank you Henrik. I need to find another way to detect when the circuit is active.

[HenrikOlsson]

Just use a simple transistor buffer.
Pullup resistor on I/O-pin, NPN transistor pulling I/O-pin to GND when the 1.2V signal drives a small current into the transitors base.

/Henrik.

[peterdeco1]

Unfortunately the circuit board is already manufactured with a pull down resistor network. The switch that activates the circuit which I'm trying to detect goes to ground when pushed. True, I can use an inverter but it needs to be a very simple hook-up. Attach B+, B-, one wire output and one wire detect. I'll probe around more today to see if there's another way around this. Again thank you Henrik.

[Charlie]

Just use the ADC to measure the voltage on the pin and decide in software what is a high and what is a low.