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RS485 is a standard defining the electrical characteristics of serial lines for use in serial communications systems. It is essentially a form of serial communication.

What is Serial Communication?

Serial communication is a way to send data. It is like the Universal Serial Bus (USB) or ethernet that we can find in many of our modern computers. Manufacturing facilities use serial communication to link their devices together. As mentioned, an example of serial communication is RS485.

There are different serial communication standards such as RS232, RS422 and RS485. The most widely used communication standard is RS232. The main difference between them is in the hardware.

About RS485

There are many standards in serial communication and RS485, also known as TIA-485 (-A) or EIA-485, is just one of them. This standard is a product of joint efforts by the Telecommunications Industry Association and the Electronic Industries Alliance (TIA/EIA). It is known for being able to be used effectively over long distances and in electrically noisy environments. Due to this and it being able to transmit data over long distances, the RS485 is used commonly as a protocol for POS, industrial and telecom. The RS485 is also common in computers, PLCs, microcontrollers and intelligent sensors in scientific and technical applications.

RS485 is used more industrially where many devices need to be interconnected together for a system. However, Arduino and Raspberry Pi hobbyists also use it for some of their projects when multiple peripherals need to be linked to the board.

Real-world applications of RS485

RS485 is used in many computer and automation systems. Some of the examples are robotics, base stations, motor drives, video surveillance and also home appliances. In computer systems, RS485 is used for data transmission between the controller and a disk drive. Commercial aircraft cabins also use RS485 for low-speed data communications. This is due to the minimal wiring required due to the wiring configuration requirements of RS485. 

RS485 is however most popularly used in programmable logic controllers and factory floors where there are lots of electrical noise. RS485 is used as the physical layer for many standards and proprietary automation protocols to implement control systems, most commonly Modbus. 

Modbus is the world’s most popular automation protocol in the market. Developed by Modicon, Modbus enables different devices from different manufacturers to be integrated into the main system. Most Modbus implementations use RS485 due to the allowance of longer distances, higher speeds and multiple devices on a single network.

Modbus devices communicate using a Master-Slave technique where only one device (the Master) can initiate transactions (AKA queries). The other devices (the slaves) respond by giving the requested data to the master, or by taking the action requested in the query. This whole system allows manufacturing facilities to control their devices remotely and also set-up automation.

How RS485 works?

Ref: lammertbies

In RS485 standard, data is transmitted via two wires twisted together also referred to as “Twisted Pair Cable”. The twisted pairs in RS485 give immunity against electrical noise, making RS485 viable in electrically noisy environments. 

RS485 at its core with 2 wires allows half-duplex data transmission. This means data can be transmitted in both directions to and fro devices one direction at a time. By adding another 2 wires, making it a 4 wires system, it allows data transmission in both directions to and fro devices at the same time, also known as full-duplex. However, in a full-duplex setup, they are limited to a master and slave communication where slaves cannot communicate with each other.

Wire Half Duplex System

 

Ref: Windmill

TX and RX refer to the transmitted signal and received signal respectively. It is also represented by the orientation of the triangles. 

In this setup both the TX and RX share a single pair of wires, therefore it is limited to half-duplex data transmission as the data cannot be transmitted simultaneously to and fro each device.

Wire Full Duplex System

 

Ref: Windmill

Similarly, TX and RX refer to the transmitted signal and received signal respectively. It is also represented by the orientation of the triangles. 

Variably, this time both TX and RX have their own 2 wires for data transmission. This means that data can be simultaneously transmitted and received between devices.

Ref: Robotiq

Devices will be linked together via a bus configuration as shown in the picture above.

Advantages of RS485

RS485 main advantages as compared to other serial communication are tolerance to electrical noise, lengthy cable runs, multiple slaves in one connection, and fast data transmission speed. 

RS485 has many advantages over other standards, especially when it comes to applications in noisy industrial environments. The design of RS485 is targeted towards it being tolerant and forgiving to noise and long cable runs with the twisted pair cable arrangement. It allows cable lengths up to 1,200m/4000feet

Another major advantage is that there can be more than one slave in the connection. Up to 32 slaves can be connected in the system. This is great for Supervisory Control and Data Acquisition (SCADA) systems where there are many devices and it also comes at a very low cost to implement.

Ref: Robotiq

Additionally, data can be transmitted at up to 10MBit/s which is faster than most standards.

These advantages compared to other alternatives made RS485 popular and used in a widespread amount of instances.

RS485 Tools

As mentioned, RS485 is used to link devices instead of other means as it provides significant advantages. However, what if you want to use RS485 in your projects but your device only has USB support? Fret not. There are tools available that can be used to convert your USB ports to RS485.

SenseCAP S2110 Grove to MODBUS RS485 Converter
  • Easily build MODBUS RS485 industrial-grade sensors: With open-source source code and IP66 enclosure, easily convert over 500+ existing Grove sensors to MODBUS RS485 industrial-grade sensors.
  • SenseCAP Data Logger and IoT Platform Compatible: Convert to a SenseCAP LoRaWAN® sensor with SenseCAP Data Logger and take advantage of quick and easy set-up in just 5 minutes with SenseCAP Mate APP.
  • Supports Third-party Data Loggers and IoT Platforms: Besides SenseCAP Data Logger, developers could connect to other data loggers that support MODBUS RS485 protocol and third-party IoT platforms.
  • Ready-to-deploy Industrial-grade Outdoor Enclosure: IP66 waterproof rate outdoor enclosure with window and waterproof ventilation hole reserved for light and gas sensors, also comes with a customized mounting panel.
USB TO RS232 / RS485 / TTL Industrial Isolated Converter
    • This converter converts a USB portto not only RS485 but also RS232 and TTL, making it more versatile.
    • It also features embedded circuits protectionfeatures such as power isolation, ADI magnetical isolation, and TVS diode.
    • It is built to last with its aluminium alloy enclosure.
    • It is unquestionably an ideal choicefor industrial equipment use due to its high speed, reliability, safety and versatility.

     

    Project done-  continues rail thermometer, weather monitoring station

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