Pulling a pin high

Siri

Is it ok to pull a pin high(connecting to + ve 3.2V directly) or do I have to use a resistor.
If so what value would I use.
Will this also return 1(high) -when INA is used to read the state of the pin.

Thanks,

Siri

Mike Green

If the I/O pin is always an input and can't ever be an output, you could tie the I/O pin to either Vdd (+3.3V) or Vss (ground). Unfortunately, if the I/O pin ever gets accidentally (though a programming mistake) set to output mode and the I/O pin state is opposite from the way you've connected it, you may instantly damage the I/O pin circuitry in the chip.

It's always much safer to use a series resistor that will limit the fault current to something the chip can handle. A minimum of 100 Ohms will work, but a 1K to 10K resistor is much better. Most circuits I've seen use something like 10K.

INA will return 1 bits for any input pins with a voltage greater than 1/2 of Vdd (1.65V usually). The Propeller datasheet gives the exact value.

Siri

Thanks Mike for the prompt reply.

Siri

Bean

In Mike's example, a low resistor value (100 ohms) would be called a "strong" pull-up.
A larger value (10K) is called a "weak" pull-up.

Bean

ErNa

In the case, that the signal is constant, a soft pull-up is sufficent. The resistor forms a voltage source with a certain output impedance, so external influences can disturb the voltage output. Normally, the input is variable and if driven by an switch to ground, the time constant created by input capacity and pull-up resistor determines the maximum signal speed. So there are two reasons to have a strong pull-up: decrease time constant of R/C filter and improve IME.

Siri

Thanks for all that info what resistor to use and when.

Siri