The RS-232, RS-422 & RS-485 or Recommended Standards EIA/TIA-232, EIA/TIA- 422 and EIA/TIA-485 of the Electronic Industries Alliance and the Telecommunication Industry Association
RS-232 only permits point-to-point connections, uses (according to the common V.24 standard) 9 or 25 pin connectors for unidirectional data-transmission and handshaking lines and the cable length should not exceed 15 meters.
RS-422 allows only one driver, but multiple receivers, uses full duplex transmission through 4 conductors and the cable length can be up to 1200 meters.
RS-485 allows buses with multiple transmitters and receivers, uses half duplex transmission through 2 conductors, where (like the RS-422) the maximal bus length can be 1200 meters.