Difference Between Serial RS-232, RS-422, RS-485 On Industrial Motherboard

- Mar 06, 2020-


RS-232 has a variety of uses in industrial motherboards, such as connecting a mouse, printer, or modem, and can also connect industrial instruments. RS-232 is limited to point-to-point communication between the serial port of the industrial motherboard and the device. The maximum communication distance is 15.24 meters.


RS-422 uses differential signals, and RS-232 uses unbalanced ground-referenced signals. Differential transmission uses two wires to send and receive signals, which can better resist noise and have a longer transmission distance, which has great advantages in the field application of industrial motherboards.


RS-485 is an improvement of RS-422. The number of connected devices is increased from 10 to 32. At the same time, the electrical characteristics of the maximum number of devices are defined to ensure sufficient signal voltage. Excellent anti-noise and multi-device capabilities. When establishing a distributed device network connected to an industrial computer, other data collection controllers, HMIs, or other operations, RS-485 is the serial connection.

Differences between RS-232, RS-422 and RS-485

RS-232, RS-422, and RS-485 are all serial data interface standards that were originally developed and published by the Electronic Industries Association (EIA). RS-232 was released in 1962 and named EIA-232-E as an industry standard to ensure compatibility between products from different manufacturers. RS-422 was developed from RS-232. In order to improve the shortcomings of RS-232 communication distance and low speed, RS-422 defines a balanced communication interface, which increases the transmission rate to 10Mb / s and the transmission distance to 4000 feet (at a rate lower than 100kb / s) It allows up to 10 receivers to be connected on a balanced bus. RS-422 is a unidirectional, balanced transmission specification for single-machine transmission and multiple-machine reception. It is named TIA / EIA-422-A standard. In order to expand the scope of application, EIA formulated the RS-485 standard on the basis of RS-422 in 1983, adding multi-point, two-way communication capabilities, that is, allowing multiple transmitters to be connected to the same bus, and adding transmitters The driving capability and collision protection characteristics of the bus have extended the common mode range of the bus, namely the TIA / EIA-485-A standard.

RS-232 is currently the most widely used serial interface for industrial motherboards. Adopting an unbalanced transmission method, the so-called single-ended communication, is designed for point-to-point (that is, only one pair of receiving and transmitting devices) communication, and is suitable for communication between local devices.

RS-485 is the same as RS-422, its maximum transmission distance is about 1219 meters, and the maximum transmission rate is 10Mb / s. RS-422 can support 10 nodes, RS-485 supports 32 nodes, RS-485 is a superset of RS-422, so all RS-422 devices can be controlled by RS-485.