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RS-232

RS-232

RS-232 is a common asynchronous Serial Communication Standard. It was developed by the Electronic Industries Association (EIA).

RS stands for Recommended Standard and it was a very common "de facto standard" until it later became an official EIA standard. The name of the standard is EIA-232, though everyone still refers to it as "RS-232". The EIA-232 standard is devided into a electrical specification (V.28) and a functional/procedural specification (V.24).

For instance this kind of communication is present between the PC (Data Terminal Equipment) and the phone line modem (Data Communication Equipment).

This standard describes the voltage levels, impedance levels rise and fall times, bit rate etc. This standard also explains the function of 25 signal and handshake pins for serial data transfer.

Most people refer only to the voltage and signal specifications when they speak of RS-232, since it's functional description is the same as the one used in other serial communications standards such as UART and RS-422.

RS-232 serial communication standard
RS-232 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 so-called parity bit may be included to provide a simple error detection mechanism.

RS-232 voltage standard
The electrical interface includes unbalanced line drivers, i.e. all signals are represented by a voltage with reference to a common signal ground. RS-232 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: Mark (logical 1)
Transmitter Voltage Range: -15V to -5V
Receiver Voltage Range:-25V to -3V


Signal State: Space (logical 0)
Transmitter Voltage Range: +5V to +15V
Receiver Voltage Range:+3V to +25V


Signal State: Undefined
Transmitter Voltage Range: -5V to +5V
Receiver Voltage Range:-3V to +3V


last edited (July 6, 2006) by Lundin, Number of views: 7639, Current Rev: 7 (Diff)

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