RS-232 is a standard communication protocol for connecting computers and their peripheral devices to enable serial data exchange. In simple terms, RS232 represents the voltage for the path used for data exchange between the devices. It determines the common voltage and signal level, common pin wire configuration and minimum, amount of control signals.
RS232 represents the signals connecting between DTE and DCE. Therefore, DTE represents Data Terminal Equipment and an example for DTE is a computer. DCE represents Data Communication Equipment or Data Circuit Terminating Equipment and an example for DCE is a modem.
RS232 was introduced in the 1960s and was initially referred to as EIA Recommended Standard 232. RS232 is one of the first serial communication standards with provided simple connectivity and compatibility across multiple manufacturers. The DTEs in RS32 are electromechanical typewriters and DCEs are modems.
The RS-232 interface works in a mixture with UART (universal asynchronous receiver/transmitter). It is a part of an integrated circuit integrated within the processor or controller. It creates bytes and sequentially sends the single bits in a frame. A frame is a defined structure, carrying a meaningful sequence of bits or bytes of data. It has a start bit followed by 8 data bits, a parity bit, and a stop bit. Once data is modified into bits separate line drivers are used to changing the logic level of UART to RS-232 logic.
Finally, the signals are shared along the interface cable at the particular voltage level of RS-232. The data is transmitted serially on RS232. Each bit is transmitted one after the other. This mode of transmission needed that the receiver is aware of when the actual data bits are appearing to synchronize itself with arriving data. Therefore, logic 0 is sent as a start bit.
The start bit in the frame signals the receiver that a new character is arriving. Once the receiver acknowledges the next five to eight bits are sent which defines the character. This is followed by the parity bit used for error detection. The parity bit can determine an even or an odd number of ones in the set of bits. For error detection, it can add a more bit to the data word.
The transmitter evaluates the value of the bit based on the data sent and the receiver also implements the same computation. It tests the parity value to the computed value. The stop bit supports the receiver to recognize the end of the message. The start bit continually has space value and the stop bit has mark value.
This generates a framing error condition in the receiving UART. The device then attempts to resynchronize on more incoming bits. At the other end again the line driver interface changes it into UART compatible logic levels. At the destination, a second UART re-assembles the bits into bytes. This is how RS232 creates the data exchange compatible and reliable.