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 Max Data Rate
40 Feet = 12m 10 Mbits/sec
400 Feet = 122m 1 Mbits/sec
4000 Feet = 1219m 100 kbits/sec

 

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 reventing contention between talkers.   

RS485A Standard
Up to 32 Driver/Receiver Pairs
Line Length Max Data Rate
40 Feet = 12m 10 Mbits/sec
400 Feet = 122m 1 Mbits/sec
4000 Feet = 1219m 100 kbits/sec

 


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