Xin/Xout ideas?

I am playing around with the Xin/Xout commands using a PIC 16F88 and TW523 powerline interface.
I thought that the TW523 was supposed to be "smart" and only transmit when no other devices are talking on the powerline.

Is there some way (zero crossing pin??) to check if the power line is clear before transmitting a signal to avoid collisions?

Any help with this question, comments regarding Xin/Xout, or sample code would be greatly appreciated.

Thanks guys.

The TW523 is about as dumb as dumb can get. Not only does it not "only transmit when no other devices are talking on the powerline", it delays it's output so that you are actually seeing what was on the powerline 22 half-cycles earlier. Think of it as a 22-bit shift register with a 120Hz clock.

There is no way to tell whether the powerline is clear before transmitting. The best you can do is to check that the output is the same as your input but this is after the fact.