RS232 and a RS485

what is the differance between a RS232 and a RS485

To describe the differences (there are two main ones) I'll also have to discuss RS-422.

1. RS-232 Uses one common reference wire. All the signal wires are measured relative to the one reference wire. The voltage on the signal wires is roughly +12 volts and -12 volts. The Transmit and Reveive signals are on seperate wires allowing simultaneous transmission in each direction between two stations.

2. RS-422 uses 2 wires for each signal. For one state, one of the wires is 5 volts lower than the other. For the other state they swap places. This provides for a 'balanced' signal which is much more imune to electrical interference than RS-232. The Transmit and Receive signals are on seperate pairs of wires allowing for simultaneous communication like RS-232. It can also have one initial transmitter with multiple receiver. The transmitter may indicate to one of the receivers that it may transmit back. As there is only one return path, only one of the initial receivers may answer at any time.

3. RS-485 can be viewed as RS-422 but with the Transmit and Receive functions happening on only one electrical pair. Obviously only one of the connected device may transmit at any one time.

There are vaious protocols which may be implemented in software or hardware to regulate the transmission and reception by stations, avoiding the simultaneous problems, or at least recovering in an organized way from these events (also called collisions). This is beyond the electrical characteristics of the communications standards.

I noticed after writing the reply that it was in the Practice Postine area, so consider this a 'Practice' reply.