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Is there a way to set an Arduino pin as being both an input, and an output?
I was looking at tristates, I'm not sure if that is related, or if there is some other method.
Perhaps I can try switching states rapidly. on one pin. I'm just not familiar with how to do it, and I don't see anything about it on the Arduino site.
This is a function of other microcontrollers, such as PICs, but I'm not sure about AVRs and Arduino types.
The source code for the 1-Wire protocol is a great place to start when learning how to use a single pin for both input and output.
See also chap. 18. I/O-Ports in the ATmega328p datasheet.
Cheers!
A tri-state pin is not both an input and an output, rather each pin can be in 1 of 3 states (High, Low, High Impedance). These are typically used on a bus, where many similar devices are connected.
AFAIK the Arduino does not support tri-state, but it is possible to implement a bus. This was done by using open collector/drain devices with a resistor pull-up.
This was a common method of implementing computer busses (more than 40 years ago with RTL logic), but suffers from slow speed, and low fan-out, due to capacitance.
It is still used for low speed short busses such as I²C and 1-wire.
In practice all devices are set as Input. When a device wants to communicate it is configured as Output.
INPUT_PULLUP state, which is a weak pull to Vcc. You can connect a pin to an open-collector bus directly and then just switch between INPUT (i.e. HiZ, to either read or write 1) and OUTPUT LOW (to write 0).
Oct 22, 2016 at 10:48