What is RS485? What is the working principle of RS485?

Post date: 18:46:00, 12/09/2021 GMT +7


What is RS485? What is the working principle of RS485?

What is RS485?

RS485, also known by its full name, is the RS485 communication standard or RS485 cable, this is a communication method that connects to computers and other devices. RS485 is not just a single interface but it is a communication complex capable of creating simple networks of many devices. The RS485 communication standard can connect up to 32 devices on a single wire pair and a ground wire system at a distance of up to 1200m.

Structure of RS485

RS485 cable is constructed very simply, only from wires twisted together in pairs. However, this very structure creates a serious drawback, when interference occurs in one pair of wires, the other pair will immediately suffer as well. This leads to the operating voltage between the 2 wires not having too much difference, the RS485 receiver can still receive the signal because the receiver has eliminated all interference.

What is the working principle of RS485?

The principle of operation of RS485 is quite simple, data will be transmitted through 2 wires when twisted together, this wire is called twisted cable. When the wire is twisted, it gives RS485 high anti-interference ability and better long-distance signal transmission.

RS485 is divided into 2 types of configuration, currently the most commonly used is 2-wire configuration and 4-wire configuration. Let's find out the working principle of these 2 types of configuration!
RS485 . cable construction

2-wire RS485 pinout

For 2-wire configuration, data will be transmitted in one direction at a given time. With this type of setup, the TX and RX signals will share a single pair of wires, helping users save on installation costs.

Looking at the figure above, we can see that the transmitter and receiver will be connected at each node of a twisted pair. However, the 2-wire configuration limits the nodes to twisted pair so the user must pay attention to the turnaround delay.
2-wire RS485 pinout

The operating principle of the 4-wire configuration is quite different, where data will be transmitted and arrived at the same time from the nodes. Here, 2 wires will take care of transmitting and the other 2 wires will take care of receiving.

Looking at the figure above, we can see that the main gate and transmitter are reconnected to the node system that receives data on twisted pairs. However, you should note that these links will be limited to primary and secondary communication, or simply limited to where nodes cannot receive signals from each other.

Advantages and disadvantages of RS485
Advantages of RS485
– Is the most advanced product today, overcoming the weaknesses left by RS232.
– RS485 cable is the only communication standard that can connect multiple transmitters and receivers on the same network at the same time.
– Receivers with input resistance up to 12kΩ RS485 can still connect up to 32 devices. In addition, with other inputs, RS485 can connect up to 256 devices.
– When RS485 is connecting devices at a fairly long distance, users can overcome it by installing more repeaters to increase the number of connected devices, making the signal more stable, avoiding line interference.
– RS485 has 2 signal lines installed, so the signal will be transmitted faster over longer and wider distances.

Disadvantages RS485
– When transmitting too many devices on the same line, the response time will be slow.
– Devices need to use the same RS485 standard instead of the existing Analog standard
– A certain knowledge is required to use RS485 effectively