RS-422 is a protocol or specification that must be followed in order to allow two devices that implement this standard to communicate with each other. It was introduced to provide higher data rates on serial data lines. The previous standard with RS-232 did not provide such indicators.
The RS-422 interface is capable of supporting data transfer rates of up to 10 Mbps at a distance of up to 15.24 m. The main reason why this standard was able to achieve such improvements is the use of differential or balanced transmission technologies.
The RS-422 uses both differential transmitters and receivers, which means that it is much more resistant to interference in general mode.
Introduction
The RS-422 interface is significantly different from RS-232, it can be used as a direct interface in many cases. Although RS-232 was the most popular standard for serial communication, the higher speeds offered by RS-422 are a clear advantage, and as a result, it is used more widely. It can also be used interchangeably with RS-232, which significantly increases the versatility of the standard.
Some systems can be directly connected using RS-422 signals. Converters are used to expand the range of RS-232 connections. The standard defines signal levels. Other serial interface specifications, such as electrical connectors and contact wiring, are set by other standards.
What is RS-422?
The RS-422 interface is the common name for the short form of the American National Standards Institute (ANSI) standard. Technical standards define the electrical characteristics of a balanced voltage digital interface circuit. The protocol provides data transmission using symmetric or differential signaling with unidirectional or irreversible, terminal or non-terminal transmission lines.
In telecommunications, RS-422 is the name of a technical standard that defines the electrical characteristics of a digital signal circuit. This is the standard for binary serial communication between devices. The RS-422 interface is an updated version of the original serial protocol standard known as RS-232. Several systems are directly connected using signals. Converters can be used to expand the range of connections. Although the RS-422 interface defines signal levels, other serial interface properties are set by other standards. In communications, one device is Data Terminal Equipment (DTE) and the other is Data Transmission Equipment (DCE).
Interface Types RS-422
There are several different types of RS-422 chips. The most common ones are classified by type of packaging, data rate, supply voltage and ESD voltage.
The most common data transfer rates are 10, 20, 50, and 60 Mbps.
Characteristics
Among the main advantages of the standard are a differential receiver, a driver and a data transfer rate of up to 10 megabits per second at a distance of up to 15 meters. Since signal quality deteriorates with the length of the cable, the maximum data rate decreases as its length increases.
Limitations on the length and speed of data transfer depend on the parameters of the wire length, balance and completion, as well as on a separate installation. Conservative maximum data rates with a UTP cable (POTS) 24AWG range from 10 Mbit / s at 12 m to 90 kbit / s at 1200 m. This indicator is a classic, based on empirical data, and not a limit imposed by the standard.
Benefits
The benefits of the standard include a differential receiver, driver, and high speed data transmission over long distances. Post-production linear editing tools and broadcast automation systems use RS-422A to remotely control players / recorders located in the central hardware room.
When choosing an RS-422 interface, consideration should be given to the following attributes:
- data transfer rates (10, 20, 50, 60 Mbps);
- supply voltage (up to 5 V) and ESD (up to 7 kV).
Application area
The most common use of RS-422 was on earlier Macintosh computers. It was implemented in a multi-pin connector, which had enough technical capabilities to support most of the common RS-232 contacts. The first models used a 9-pin D connector, but it was quickly replaced by a mini-DIN-8 connector. They were used both to support RS-232 devices, as well as for AppleTalk networks, RS-422 printers, and other peripheral devices. Two of these ports were part of every Mac until they were replaced with ADB Universal Serial Bus ports on the iMac in 1998.
Broadcast automation systems and post-production line editing tools use RS-422A to remotely control players / recorders located in the central hardware room. In most cases, Sony uses a 9-pin connection, which uses the standard DE-9 connector. This is the de facto industry standard RS-422 interface connector used by many manufacturers.
RS-422 and 485 interface splitter: comparison
RS-232 is the most common serial interface and is used for sending as a standard component on most Windows-compatible desktop computers. Now the converter of RS-422 interfaces to the CAN converter via USB is more often used with the help of a converter that supports only one transmitter and one receiver on each line. It also uses the Full-Duplex transmission method. Some boards support data transfer rates of up to 1 Mbps, but most devices are limited to 115.2 kbps.
Disadvantages of RS-232:
- short distance - cable length is limited to 15 meters;
- susceptibility to interference;
- lack of multifunctionality.
The RS-422 interface for dummies (EIA RS-422-A standard) is a serial connection. Provides a data transfer mechanism of up to 10 Mbps. Sends each signal using two wires to increase maximum transmission speed and cable length. The RS-422 interface is also defined for multi-tasking applications in which only one transmitter is connected to the bus with up to 10 receivers and transmits it.
RS-485 is a superset of RS-422 and extends its capabilities. It was made to address the multiple drop limit of RS-422, allowing 32 devices to simultaneously exchange data on the same transmission line. Any of the slaves on the RS-485 bus can communicate with any other 32 slaves without going through the master.
Technology evolution
RS-422 is similar to RS-232, and it can be programmed in the same way, however, it also has several advantages and disadvantages. One of the problems is that you need to purchase an RS-422 to RS-232 converter, as it is not included in the standard PC package. Some advantages of the RS-422 interface, description and connection:
- Long distances - supported up to 152 meters, and with amplifiers you can achieve even greater distances.
- MultiDrop - for each port, you can connect up to 32 devices and even more with amplifiers. Devices have unique addresses that are assigned to each device. For example, if 5 devices are connected to the port, they will be addressed to units 1-5. If you want to contact block number 1, you send a command to block number 1. All units will see this command, but only the device address will respond. This also applies to RS-485. Addresses can be set using switches or software, depending on the design of the device.
- Noise immunity - since the standard uses a separate pair for reception, it provides better noise immunity than RS-232.
RS-485 is very similar to RS-422. So much so that it often causes confusion. Both technologies are multithreaded and allow data to be transmitted over very long distances. The differences are that the RS-485 is a 2-wire system as opposed to the 4-wire RS-422 interface.
Distinctive features of standards
The main differences between the RS-422 and 485 PR-6 interface splitters:
- RS-485 can have several command devices and several listening devices. RS-422 can have only one Commander and several listeners. For example, you can connect one PC (command device) to 10 temperature controllers (listeners). The PC can instruct any of the controllers to change the setpoint or send temperature readings, but none of the controllers can command any of the other controllers. With RS-485, you can have multiple PCs and multiple controllers on the same bus. One PC can send a command to change the set value, and another computer can send a command to send data.
- RS-485 wiring is simpler because only 2 wires are used.
- RS-485 programming is more complicated because data is sent and received on the same two wires. You must turn the transmitter on and off at the right time to ensure proper communication.
Cable specifications
How to check the RS-422 interface? In addition to the obvious features of cable specifications, they include several prerequisites:
- Characteristic impedance is a value based on the inherent consistency, resistance, capacitance and inductance of the cable.
- Shunt Power - The amount of equivalent capacitive load on the cable. One factor limiting the overall cable length is capacitive loading. Longer systems allow for the use of cable with small capacitance.
- Propagation speed - the speed at which an electrical signal travels in a cable. The value given should usually be multiplied by the speed of light to obtain units of measurement per second. For example, a cable indicating a propagation velocity of 78% gives a speed of 0.78 x 300 x 106-234 x 106 m / s.
Differential drivers
Line drivers and receivers are used to exchange data between two or more points on the network. Reliable data transmission can be difficult in the presence of induced noise, differences in grounding levels, impedance mismatches, the impossibility of effective bias for inactivity conditions and other hazards associated with the installation of the network.
Standards are designed to ensure the compatibility of devices provided by different manufacturers, and to ensure success in transmitting data over specific distances and at certain speeds.
The balanced voltage digital interface circuitry is typically used on data, time, or control circuits, where the information transfer rate is up to 10 Mbps. Devices with a digital interface with symmetrical voltage, corresponding to electrical characteristics, should not work in the entire range of data transfer speed.