What does it mean to "tristate a pin" on a CMOS microcontroller?
Answer
"Tristate" means a state of high impedance. A pin can either pull to 0 V (sinking current, generally), pull to 5 V (sourcing current, generally), or become high impedance, like an input.
The idea is that if a pin is in high impedance state, it can be pulled to high or low by an external device without much current flow. You see this kind of thing on bidirectional serial lines, where sometimes a pin is an output and sometimes an input. When it's an input, it's "tristated," allowing the external chip to control its logic level.
Does that make sense in your situation?
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