RS-232 and RS-485

The Electronic Industry Association’s RS-232 is the oldest and still most widely used standard for exchanging data between two devices. A vast array of equipment has RS-232 ports available.

RS-232 serial communication transmits data one bit at a time over a single data line. Single data bits are grouped together into a byte and transmitted at a set interval, or baud rate. Serial transmission can be over a simple connection consisting of 3-wires of transmit, receive, and ground signals.

A benefit of RS-232 is the ability to coordinate communication between a fast controller and a slow serial device using the RS-232 RTS and CTS hardware signals for “handshaking.” This ensures both devices are in sync so data is not lost.

Also very common in control applications is RS-485. You can think of RS-485 as an industrial-strength version of RS-232. Among the numerous improvements are more noise-resistant balanced lines (2-conductors), longer transmission distances (up to 4,000 feet at 9600 bps versus 30-50 feet for RS-232), and multidrop connections between several devices instead of just two.