Jan 29, 2011

What is Difference Between RS232 & Rs422/RS485

RS232 and RS485 Port are available on every PLC for communication with external devices. RS stands for Recommended Standard. There are many differences between Rs232 and RS485/Rs422. Here in this post we will see the major differences between them and also see what DTE and DCE means .

What is the Difference Between RS232 and Rs422/RS485 :-
As we all know RS232 and RS485 both are used for serial communication but still many us have the confusion in understanding the exact difference between them , the major differences are as below.

<1> RS232 is single ended communication i.e in RS232 there is one transmitter and one receiver whereas RS485 is differential communication i.e it can have up to 32 transmitters and 32 receivers. Accordingly single ended cabling in Rs232 and Multi-drop Cabling in RS485.

<2> RS232 is used for small distances up to 50 ft with maximum speed up tp 19.2 Kbps whereas in RS485 speed up 100Kbps can be achieved for distances up to 4000ft.

<3> RS232 has Unbalanced Signaling Mode whereas RS485 has Balanced Signaling Mode.

<4> In RS232 Communication Mode is Full Duplex whereas in RS485 both Half Duplex and Full Duplex Communication can be achieved.

<5> In RS232 the output current is 500mA whereas in RS485 the output current is 250mA.

<6> Maximum Driver Output Voltage in RS232 is +/- 25V compared to -7V to +12V in RS485.

<7> Driver Load Impedance (Ohms) is 3k to 7k in RS232 whereas in RS485 Driver Load Impedance is 54k.

What is Unbalanced and Balanced Signaling Mode :-

RS232 has Unbalanced Signaling Mode i.e Unbalanced signal is represented by single signal wire where the voltage level is with respect to some system common/ground to transmit/receive binary 0 and 1. It can be considered as push signal driver.

RS485 has Balanced Signaling Mode i.e balanced signal is represented by paired wires so that the voltage difference between these two is used to transmit/receive binary values.It can be considered as push-pull signal driver.

Important Note :- An unbalanced voltage signal travels slower and shorter than a balanced voltage difference signal. So this is the main reason for faster speed inn RS485.

If still have any doubts regarding RS232 and RS485 , you can write in comment section.
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