Overview of the physical structure of RS232

The serial, asynchronous RS232C or V.24 communication interface is a widely used as a simple physical connection for exchanging data between two systems. The RS232 interface only describes the physical structure and not the protocol or the application layer.

The data are applied sequentially for the duration of one bit. Synchronization is based on start and stop bits. Asynchronous data transfer requires no clock line. This means that a minimum of 3 lines are required, i.e. one for sending, one for receiving, and one for GND. Since in each case one line is available for sending and one for receiving, the technique is referred to as full duplex transfer. All devices can send or receive as required, since they have a dedicated line available.

The RS232C or V.24 interface operates bipolar with +12 V / -12 V voltage level (+3 V...+12 V = "0" and -3 V...-12 V = "1" ). The same baud rate, number of data bits, number of stop bits, and data verification of the so-called parity bit have to be used on both sides. This is usually described as 9600, 8, e, 1 (i.e. 9600 baud, 8 data bits, even parity verification, one stop bit).