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How To Use RS232 to RS422 Converters

In a world of Internet broadband and high-speed local area networks, there remain valid reasons for deploying RS232 to RS422 converter products in environments where required throughput is measured not in Mbps, but in Kbps.
For example, one reason is to extend the physical distance over which devices with RS232 interfaces can operate. And another is to allow conversion between different signaling protocols (especially common with legacy printer and automated manufacturing solutions.)
This article looks at how to achieve and meet these requirements by using relatively inexpensive RS232 to RS422 Converter units.

But first, a brief recap of RS232 and RS422.
The RS-232c specification has been around for decades and has supported synchronous and asynchronous data transmission between modems, printers, personal computers and other data communications devices. Using either 25 pin or 9 pin connectors, it’s possible to transmit and receive data at speeds of up to 20 kbps as long as the distance doesn’t exceed 50 feet, or approx 15.2 meters. (Note that modern devices do support transmission rates beyond 20 kbps but this is outside the RS232c Standard’s scope. Support for longer distances is also possible with lower-capacitance cables.)

Extending the transmission distance up to nearly 4000 feet (1200m) is possible with a RS232 to RS422 converter. By the way.. a USB to RS422 converter, which is often more convenient, can in most cases be used in place of a RE232 to RS422 converter. This is because the RS422 converter specification (effectively the successor to the RS232 standard) uses a balanced four-wire system with one pair of wires handling DTE-DCE transmission, and the other DCE-DTE transmission.
Most portable RS232 to RS422 converter units support full duplex (bi-directional) speeds ranging between 300 bps and 115 kbps, with power being provided from the RS232 / RS422 converter port (although external power supplies can be connected to some models, if needed.)

On the RS232 side of the converter the connector is often a DB-9 female and on the RS422 side of the converter is usually a DB-9 male, or a multi-way terminal block implemented. When using a RS232 to RS422 converter the maximum RS232 length at both ends is still restricted to 15.2 meters, while the intermediate RS422 converter side connected cable can range up to 4000 feet (1200m). However, even although transmitting differential signals on balanced lines of twisted pair copper cables can achieve higher data throughput rates in electrically noisy environments, it’s recommended to run a signal ground across the RS422 converter. Note that a pair of converter units will normally be required unless the far-end device already supports RS422.
In various industrial automation environments it’s necessary for a host/PC to communicate with devices that are not LAN-aware but are capable of supporting communications over a RS422 converter interface. This is where a Master/Slave multi-drop RS422 converter configuration can be used to control up to 32 devices over a distance of 4000 feet (1200 meters.)

Some RS232 to RS422 converter models are designed to support only up to 10 multi-drop RS422 converter receiver devices and with effective throughput of probably less than 100 kbps. Consideration will also need to be given to the termination resistance at the RS422 converter receiver end and to the connection of Protective Grounding and Signal Grounding, as per the RS422 converter Standard recommendations.

Visit USconverters.com to find out more about RS232 to RS422 converter products, free Tools and Diagnostic software, in addition to the RS232 to RS422 Converter User Manual.


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