Tri-state logic on IO pins?

Forum 2005-2010 (read only) Hardware Interfacing
1

Since the digital IO pins can be used for I and O :wink: Can their direction be changed as necessary to accommodate/emulate a tri-state output?

I have a specific need to either ground the pin's output or let if go to a high impedance so that the device I'm controlling can rise to well above 5V. (I can protect the Arduino pin from unhealthy voltages.) But I need to know if this is a valid use of the pin input/output setting.

And would I need to address the built-in pull-something resistor?

Thanks!

2

The pinMode function can be used to put pin into a quasi Tri-state mode by setting it to input mode. When mode is set as output then either a high or low can be generated with the digitalWrite function. I believe the best way to ensure that the internal 'soft' pull-up is disabled is to make the output state a low before setting the mode to input.

Lefty

3

digitalWrite( pinNumber, LOW );
pinMode( pinNumber, OUTPUT ); // now we're sourcing current, i.e. GND
pinMode( pinNumber, INPUT ); // now we're tri-stated
pinMode( pinNumber, OUTPUT ); // and back again

4

Cool, so flipping the pinMode back and forth between input and output (very rapidly) is not going to harm anything then?

5

Cool, so flipping the pinMode back and forth between input and output (very rapidly) is not going to harm anything then?

Nothing except maybe your brain during checkout and troubleshooting time :wink:

Lefty