What is the difference between RS422 communication and RS485 communication?

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RS422 Standard

The RS422 Standard defines a serial communications standard. RS422 is a high speed and/or long distance data transmission. Each signal is carried by a pair of wires and is thus a differential data transmission system. Over distances up to 40 feet the maximum data rate is 100 Kilobytes per second. A 120-ohm resistor should be used to terminate the receiving end of the line. It is generally used between one transmitter receiver pair to ONLY one other transmitter receiver pair but each output can drive up to 10 receivers.

RS422A Standard – 1 Driver & Up To 10 Receivers
Line Length (Feet)Line Length (Meters)Max Data Rate
40ft12m10Mbits/sec
400ft122m1Mbit/sec
4000ft1219m100Kbits/sec

RS485 Standard

The RS485 Standard is similar to the RS422 standard upon which it is based. The main difference is that up to 32 transmitter receiver pairs may be present on the line at one time. A 120 Ohm resistor should be used to terminate either end of the main line. If more than one device may transmit data, the RTS line is used as a transmit enable signal, so preventing contention between talkers.

RS485A Standard – Up To 32 Driver/Receiver Pairs
Line Length (Feet)Line Length (Meters)Max Data Rate
40ft12m10Mbits/sec
400ft122m1Mbit/sec
4000ft1219m100Kbits/sec

 

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