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The RS232 standard is defined by the EIA/TIA (Electronic Industries Alliance / Telecommunications Industry Associations). The standard defines an asynchronous serial data transfer mechanism, as well as the physical and electrical characteristics of the interface.


RS232 uses serial bit streams transmitted at a predefined baud rate. The information is separated into characters of 5 to 8 bits lengths. Additional start and stop bits are used for synchronization, and a parity bit may be included to provide a simple error detection mechanism.


The electrical interface includes unbalanced line drivers, i.e. all signals are represented by a voltage with reference to a common signal ground. RS232 defines two states for the data signals: mark state (or logical 1) and space state (or logical 0). The range of voltages for representing these states is specified as follows:


Signal State

Transmitter Voltage Range

Receiver Voltage Range

Mark (logical 1)

-15V to -5V

-25V to -3V

Space (logical 0)

+5V to +15V

+3V to +25V


-5V to +5V

-3V to +3V


The physical characteristics of the RS232 standard are described in the section RS232 Connectors / Pinout