Guide to using RS232 to RS485 Converter

You probably have heard of RS232 which is a serial communication method between computers and devices, but have you heard of the RS485 communication?

The great thing about standards is there are so many to choose from. It holds true for electrical interface standards as well. As serial-data standards tend to evolve separately within particular industries, we thus have more standards than we should.

Perhaps the most successful serial-data standard for PC and telecom applications is the RS-232. Similarly, the RS-485 and RS-422 are among the most successful standards for industrial applications, however, it is often necessary to communicate between the standards. 

What is RS485?

● The RS485 is also known as TIA-485 (-A) or EIA-485 is a serial communication method for computers and devices similar to the RS232.

● Not only is RS485 a single device-to-device interface, but it is also a communication bus that is used to form a simple network of multiple devices.

● RS485 allows multiple devices of up to 32 to communicate at a half-duplex on a single pair of wire plus a ground wire at distances up to 1200 meters.

If you wish to extend the length of the network and number of nodes, you can easily do that by using repeaters.

● RS485 is used commonly as a protocol for POS, industrial, telecom and especially in noisy environments due to its wide common-mode range which enables data transmission over long cable lengths in noisy environments. The RS485 is also common in computers, PLCs, microcontrollers and intelligent sensors in scientific and technical applications.

What are the advantages of RS485?

● RS485 compared to other interfaces is probably the only one that is able to inter network multiple transmitters and receivers in the same network.

● With the RS485, you can also connect many devices to the network.

1. With the default RS485 receivers with an input resistance of 12kw, you are able to connect 32 devices.

2. With any high resistance RS485 inputs, you can connect up to 256 devices.

3. With RS485 repeaters, you can further increase the number of devices over long distances as well!

● In addition, with its arrangement (two wires are required for each signal), signals can be transmitted faster over great distances.

The RS232 to RS485 converter

The RS232 to RS485 converter is a unique device for it contains both RS-232 and RS-485 receivers and transmitters. This wide range of communication devices contained within a single IC enables an individual to convert bi-directionally between RS-232 and RS-485 signals.

Many converters from RS-232 to RS-485 are “port-powered converters” in which the RS-485 power is derived from the RS-232 RTS line (or sometimes a combination of the RTS and CTS (DTR) lines). Because the power available from an RS-232 port is limited, the RS-485 launch voltages are not achieved when using a port-powered converter with, for example, one hundred RS-485 terminations. The low receiver threshold, however, allows a fair margin for error. This technique is acceptable in systems with short line lengths and without termination resistors across the A-B terminals.

RS232, RS422, and RS485 are simple asynchronous serial protocols used in a wide range of commercial, industrial and military applications. All three use the same basic logical protocol but vary in their physical implementation, i.e., voltage levels and signaling. Since both protocols are commonly used for the same or similar applications, it is often desirable or necessary to provide signal conversion between them. In many cases, the conversion is required to interface an RS422/RS485 device to the RS232 port on a PC.