1. RS 232 is a standard developed by Electronics Industry Association (EIA).
2. This is one of the oldest and most widely used serial communication standards.
3. It is used for communication between DTE (computer) COM port and DCE (modem) port. DTE stands Data Terminal Device and DCE stands for Data Communication Device.
4. Protocol- full duplex, serial communication, Asynchronous
5. Speed is generally up to 9600 bad/sec. As the length of cable increases the speed decreases.
6. Logic levels for Receiver are -3V to -25V (Logic 1) and +3V to +25 (Logic 0). For the Transmitter the logic levels are -5V to -15V (Logic 1) and +5V to +15V (Logic 0)

RS 232 - DB Connector

1. DTE normally comes with a Male Connector, while DCE comes with a Female Connector.
2. However, that is not always true. Use the simple way below to confirm: Measure Pin 3 and Pin 5 of a DB-9 Connector with a Volt Meter, if you get a voltage of -3V to -15V, then it is a DTE device. If the voltage is on Pin 2, then it is a DCE device.

RS 232 Signals-

1. The graphic above illustrates a typical RS-232 logic waveform (Data format: 1 Start bit, 8 Data bits, No Parity, 1 Stop bit). The data transmission starts with a Start bit, followed by the data bits (LSB sent first and MSB sent last), and ends with a "Stop" bit.
2. The voltage of Logic "1" (Mark) is between -3VDC to -15VDC, while the Logic "0" (Space) is between +3VDC to +15VDC.
3. RS-232 connects the Ground of 2 different devices together, which is the so-called "Unbalanced" connection. An unbalanced connection is more susceptible to noise, and has a distance limitation of 50 ft (which is around 15 meters).