A bit is either 1 or 0, but a digital wire can express 3 states: power, ground, and high-impedance/floating (high-Z).

A half-bit carries less information, most commonly either 1 or high-Z.

As a few of you know, the interrupt line is implemented as a single line with a resistor tying it to ground (putting a 0 on the line). If a device wants to request interrupt, it un-blocks its tristate on the pin and puts a 1 on the line.

A high-impedance detector may be built with two diodes and two resistors.  The circuit returns 1,1 if the input is 1; 0, 0 if the input is 0; and 0,1 if the input is floating.

''My understanding of "high-impedance detector" is that it converts a tristate output to a bistate output by mapping high-Z to 1 or 0.  Therefore, where do your "1,1" and "0,1" outputs come from?  I presume by "un-blocks its tristate on the pin and puts a 1 on the line", you mean the output switches from high-Z to 1?''

''By the way, I've removed some extraneous material like sizes of resistors ("large" -- how big is large?) and reference to circuits burning up.''

The high-impedance detector I described has two bits of output because it is also the decoder for expressing the three distinct signal values to traditional circuits.

''By "traditional circuits", do you mean bistate logic?''

''Do you mean the following truth table?''

 Input OutputA OutputB
   0      0       0
   1      1       1
  HiZ     0       1

Yes and yes.