What Is a RS 485 Transceiver?

Geisha A. Legazpi

A recommended standard 485 (RS 485) transceiver is an integrated circuit that sends and receives digital signals directly between digital equipment, and uses positive and negative 5 volts direct current (VDC) maximum. It may be connected as a simple point-to-point or as multipoint connection so that two or more devices may communicate. The purpose of this transceiver is to make high-speed communications possible in electrically noisy environments, such as industrial plants. Without the RS 485 transceiver, the data speed and distances between communicating equipment would be much less. Multipoint operation is another good reason for using the RS 485 transceiver.

Woman holding a book
Woman holding a book

Digital transceivers generally use a direct current to send serial data to a distant receiver. When the speed of the transmission is high, the time it takes for voltage to rise and drop in a capacitive line becomes very significant. Capacitive effects happen when there is a close proximity between the sending line and the common line or signal ground. To decrease the rise and fall times, the manufacturers of the RS 485 transceiver use two output lines that are opposite in polarity all the time. This opposite polarity cancels the electromagnetic buildup on the transmission line, resulting in better signal rise and fall time performance.

The RS 485 transceiver uses +5 VDC and –5 VDC alternately for each of the two output lines. The output line can either be non-inverting or inverting. The non-inverting output is the same polarity as the input. The non-inverting line is a good reference because it is a closer replica of the input data. The inverting pin is opposite in polarity to the input.

Buying a RS 485 transceiver is easier by ordering online. The different types of transceivers available include integrated circuit versions for the more technically inclined and plug-in type adapters that may be used by more users. Contacting the vendor could be a good idea if someone is in doubt as to the correct type of transceiver to buy.

One factor in choosing a RS 485 transceiver is the signal standard on the equipment. The equipment could be using universal serial bus (USB), RS 232, or RS 422, and any of these can be connected to a RS 485 transceiver. There are readily available RS 485 adapters for various serial communications as well. Using a RS 485 transceiver is very simple because once it is installed properly, the only thing to operate on it is the power on/off switch if it has one.

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