zubair136

Difference between RS232, RS485 , RS422

4 posts in this topic

i am new in plc programming . i know the basics difference between the rs232, rs422, rs485. but i am little bit confused in it. so i have the following question regarding these terms.

1.  can these protocols communicate with each other i mean rs232 can communicate with rs422 or rs485 and same.

2. my plc has port rs422  but i can connect it with my laptop serial port which is rs232 ?

3. what are the main important points that kept in mind during communication or cross communications.

 

any help will be greatly appreciated.

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34 minutes ago, zubair136 said:

i am new in plc programming . i know the basics difference between the rs232, rs422, rs485. but i am little bit confused in it. so i have the following question regarding these terms.

1.  can these protocols communicate with each other i mean rs232 can communicate with rs422 or rs485 and same.

2. my plc has port rs422  but i can connect it with my laptop serial port which is rs232 ?

3. what are the main important points that kept in mind during communication or cross communications.

 

any help will be greatly appreciated.

1. RS-232/RS-422/RS-485 are media cable not protocol that mean if you have same cable diagram and same protocol (e.g. Modbus RTU) you can communicate with them but if you need to use RS-232 port to communicate with RS-422/RS-485 there are RS-232 to RS-422/RS-485 converter as Moxa or other brands (see detail as link below)

https://www.moxa.com/product/TCC-100.htm

2. You need to use RS-422 port but I think if you means Mitsubishi FX PLC you can use these cable diagram to connect with PC RS-232 port.

http://forums.mrplc.com/uploads/monthly_2016_02/56b91940e357a_MitsubishiCable.jpg.8fa1c7643090796c7e0436381c3d78a2.jpg

3. important that wiring diagram sometimes you should swap cable at RS-232 pin 2 to 3 and vice versa and noise in system if you had it you should select converter that have isolator.

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RS232 is usually a 1:1 communication. This means that you have one master asking questions of the slave, who can only answer the question.
RS422 / RS485 are usually a 1:N communication. This means that you have one master asking questions to several slaves that can answer only when they are addressed.

http://www.rfwireless-world.com/Terminology/difference-between-RS232-RS422-and-RS485.html

The above link may also help you out with these media types.

Regards,
Garry

 

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RS-232 is a voltage level detected communication with at least three wires (RX, TX and Gnd) between two units, Master <-> Slave, Max distance is 15 meters.

RS-485 is a current loop simplex communication with normally two wires (A and B) between a master and several (32) slave units, Max distance is 1200 meters.

RS-422 is similar to RS-485 except here we have four wires (A1, B1 + A2, B2) and the possibility of duplex communication, 10 slave units,  Max distance is 1500 meters.

Google and you'll find very useful information at wikipedia

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