The advantage of the RS485 protocol is that this it can transfer data over longer distances, up to 4000 feet, and have up to 32 nodes per single network, and it can be used for multi-point networks where multiple serial devices are setup in a bus network. some are isolated some are not, some has more than one RS485 port, some has LED lights for indicating RX/TX data flow, some are port-powered and some needs an external power supply, some are industrial strength, some are consumer products. Some of these converters can convert from RS232 to both RS485 and RS422 however many standard models only has one of the protocols. Many port-powered RS232 to RS485 converters provides an option for supplying external power. If in doubt, use an externally powered converter, then you are sure that it gets sufficient power. I using for example a USB to Serial adapter these same assumptions can be applied. RS232 to RS485 converters can be either isolated or non-isolated. An isolated RS232 to RS485 converter have optical isolators separating the data lines inside the unit, this prevents noise, high voltage spikes, surges and ground-loops from damaging your computer or the equipment you have connected to the converter. Some RS232 to RS485 converters even have the externally power supply isolated from the rest of the converter to provide additional protection. Usually isolated converters are only used if the user wants to additionally protect the equipment connected to the network (in case the equipment is of high value), or if there are reasons to suspect high voltage spikes or similar in the network.

In some cases, if the communication distance is long (above 1000 feet) and if the baud rate is over 115kbit it is recommended to put a resistor (typically 100 ohm) at the RS485 node (across the A and B lines). Adding the termination resistor does however dramatically increase power consumption so it should not be done, and is mostly not needed at shorter distances. Due to the increased power consumption termination is also rarely done when using port-powered converters.

When should I use a RS232 to RS485 converter?

The serial RS232 to RS485 converter and RS232 to RS422 converter units, also called serial converters, are small electronic devices used to convert a serial RS232 signal, (for example the COM port in older computers) into either RS485 or RS422 signals. The typical serial converter does this in both directions which is also referred to as a bi-directional converter.

The RS422 converter is used for data transmission, using balanced or differential signaling, it is mainly used in industrial and commercial environments since lots of process equipment and machinery have this protocol built-in. The RS232 - RS422 converter is also often used in older serial devices such as older PLC's and terminal equipment. What is called 'Automatic Send Data Control', which controls the data flow, is strongly recommended for most applications and devices, this feature is built into most modern RS232 to RS485 converters.Okay, so how do you connect a RS232 to RS485 converter? The RS232 to RS485 converter can be used for point-to-point connections (connecting one RS232 to RS485 converter directly to another RS232 to RS485 converter) and point-to-multipoint networks (connecting one RS232 to RS485 converter to multiple RS232 to RS485 converters.