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Difference between RS232 RS422 and RS485-RS232 vs RS422 vs RS485 serial interfaces

This page on RS232 vs RS422 vs RS485 describes difference between RS232, RS422, RS485 serial interfaces. The difference between various terms and serial interfaces are also mentioned. All these are known as serial interfaces used for transmission of data at short distances. These interfaces are popular for monitoring and control applications.

RS232 interface

Before the introduction of USB and PS2 interfaces RS232 interface was very popular for connecting mouse, modem and printer with the computer. RS232 is a single ended serial interface which allows one transmitter and one receiver to be connected together for transfer of data.

On DB9 connector pin numbers 2 is RxD and 3 is TxD and hence in order to connect two devices interface cables need to have following cross connections.

(DB9) <-------->(DB9)
2(RxD)<-------->3(TxD)
3(TxD)<-------->2(RxD)

On DB25 connector pin numbers are 2(TD) and 3(RD). Hence following wiring connection need to be made to connect RS232 DB9 with DB25 connector.

(DB9) <-------->(DB25)
2(RxD)<-------->2(TD)
3(TxD)<-------->3(RD)

RS232 interface uses full duplex method of transmission. It can transfer data at the rate of 1 Mbps to a maximum distance of about 50 feet.

RS232 interface Features:
Cabling technique: single ended
Communication mode:Full duplex
No. of devices: 1 transmit and 1 receive
Maximum distance: 50feet at 19.2 Kbps rate
Maximum data rate: 1Mbps upto 50 feet distance
Mark (Data '1'): -5V min. and -15V max.
Space (Data '0'): 5V min. 15V max.
Signalling: unbalanced

Read more on RS232 interface pin diagrams for DB9 and DB25 connectors.

RS422 interface

This RS422 interface is used to transmit data at higher speed and for larger distance compare to RS232. This is possible due to differential mode of transmission. It uses twisted pair cable for transmission. Hence noise is reduced to great extent. It uses voltage difference between the two lines to represent binary one and zero. With RS422 interface one device acting as master can control upto 10 slave devices. This serial interface can transmit data at 10Mbps rate for distances upto 50 feet and at 100 Kbps data rate for distances upto 4000 feet.

RS422 interface Features:
Cabling technique: single ended multidrop configuration
Communication mode: Full and half duplex
No. of devices: 1 transmitter, 10 receivers
Maximum distance: 4000 feet (at 100 Kbps rate)
Maximum data rate: 10 Mbps(at 50 feet)
Mark (Data '1'): 2V min. (cable 'B' > cable 'A'), 6V max. (A > B)
Space (Data '0'): 2V min.(A > B), 6V max.(A > B)
Signalling: Balanced

Read more on RS422 interface pin diagram.

RS485 interface

This 485 interface is upgraded version of its predecessor RS422. It expands capabilities of RS422 and hence one device can control upto 32 devices. It is similar to RS422 interface.

RS485 interface Features:
Cabling technique: Multidrop
Communication mode: half duplex and full duplex
No. of devices: 32 transmitters, 32 receivers
Maximum distance: 4000 feet(at 100 Kbps)
Maximum data rate: 10 Mbps(upto 50 feet)
Mark (Data '1'): 1.5V max.(B>A)
Space (Data '0'): 1.5V max.(A>B)
Signalling: Balanced

Read more on RS485 interface pin diagram.



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