How can I read a tristate output with microcontroller?
You could tie it to ground and Vcc with two 10k resistors, and use an A/D input to read the level.

If you don't have an A/D to spare connect it to another pin of your uC with a 10k resistor. If the pin is either high or low it will of course read as high resp. low (assuming it can drive a 10k load). If it is high impedance it will read equal to what you output on the other pin.