RS485 uses twisted pair (A+, B-) signaling, just like RS422 (but, unlike RS422, it supports multiple 'masters' on the same bus), often with a ground (shield) wire (C). Full duplex uses 2 pairs, one for Tx the other for Rx, however bi-directional 'half-duplex' is supported over a single pair (so is more common, especially for long cable runs, which can be up to 1km !). Driver voltages are typically +/-2.5v to +/-5v (max +/-6v) = the minimium 'specified' reciever difference is +/- 1.5v however most work down to +/-200mV (the max. voltage, refernced to chip ground, on any pin is -7 to +12). 'Idle' state is usually A more positive than B (which is taken as a '1') and (since the drivers are 'tri-state', idle is 'guaratneed' with the use of 'bias' resistotrs). You can, in fact, 'get away with' using TTL 0,+5 and +5,0 as the two states
RS485 is used for the 'Profibus' and 'Modbus' interface standards, and extensivly used for CCTV camera control (for example,