Main Differences Between RS-232, RS-422, and RS-485

Over the years, many customers have asked us to provide more information about the differences between the three main serial interfaces commonly in use today, RS-232, RS-422 and RS-485. This article will be addressing this question specifically.

RS-232 serial interface

RS-232 Pinout

RS232 was first introduced in 1962, This is the most common type of serial interface, it was the standard communication before the PS2 and USB became popular in the computer industry. You use it to connect mouse, modem and printer to RS232 serial interface. RS232 only allows for one transmitter and one receiver on each line. RS232 also uses a Full-Duplex transmission method. RS232 can transmit up to 1Mbps with maximum distance up to 50 ft.


 

RS-422 serial interface

RS-422_485_Pinout

RS422 is an improved version of RS232 which uses twisted pair cables to reduce the noise, and it uses signaling balancing to transmit data. The signal becomes balanced – It uses a voltage-difference between the two lines as an indication of the signal value, with this method the data is able to transmit for a longer distance with faster data rates. With RS422 the data can transmit up to 10 Mpbs at 50 feet or 100 Kbps at 4000 feet. RS422 is capable of multi-drop capability which it limits up to 10 slaves in the data line.

 

 

RS485 serial interface

RS485 is an improved version of RS422, it expands on the capabilities. The major change is to have multi-drop Limitation of RS422, allowing up to 32 devices to communicate through the same data line. Any of the slave devices on an RS-485 bus can communicate with all the slave devices within the data line without going through a master device.

2wire rs-485


Quick Comparison Chart

For your easy reference, we have prepared a quick comparison chart to demonstrate the key differences of these 3 commonly used serial interfaces for industrial applications. Hope you will find this chart useful and please let us know if you have any additional question.

 

RS232

RS422

RS485

Cabling

single ended

single ended multi-drop

multi-drop

Number of Devices

1 transmit 1 receive

1 transmitters 10 receivers

32 transmitters 32 receivers

Communication Mode

full duplex

full duplex, half duplex

full duplex, half duplex

Max Distance

50 feet at 19.2 Kbps

4000 feet at 100 Kbps

4000 feet at 100 Kbps

Max. Data Rate 1Mpbs for 50 feet

10 Mpbs for 50 feet

10 Mpbs for 50 feet

Signaling

unbalanced

balanced

balanced

Mark (data 1)

-5 V min. -15 V max.

2 V min. (B>A) 6 V max. (B>A)

  1. 5 V max. (B>A)

Space (data 0)

5 V min. 15 V max.

2 V min. (A>B) 6 V max. (A>B)

  1. 5 V max. (A>B)

Input Level Min.

+/- 3 V

0.2V difference 0.2V difference

Here are the device servers with the above mentioned functions.

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