RS232 Pin Diagram : Guide to RS232 Serial Communication

The RS-232 serial interface is a standard for serial communication that defines the electrical characteristics and timing of signals, as well as the meaning of signals for connecting computers, peripherals, and other devices. Developed in the 1960s, RS-232 was widely used in computer serial ports and remains in use in various applications.

It supports data transfer rate from about 110bps to about 115200 bps (bits per sec). Hyper terminal is the application mainly used to check serial communication port of the computer, often referred as COM port.

The interface is two types DB9 and DB25 pin connectors. The interface is mainly used for one to one serial communication for example computer to dial up modem connection.

DB25 and DB9 connector pin diagram of RS232

RS232 interface DB9 RS232 interface DB25

Figure 1 and 2 depicts RS-232 pin diagrams for DB9 and DB25 connectors. As shown in the figure, it carries both data and control signal lines. These are mentioned below.

RD- Receive data, it receives data from DCE (Data communication Equipment) and pass to DTE (Data Terminal Equipment). For example, DTE is the computer and DCE is the modem connected to the telephone line.
TD- Transmit data, it carries data from DTE to DCE.
CD- Carrier Detect, signal from DCE to DTE. Indicates that modem (DCE) is busy i.e. already using the line.
RI- Signal from DCE to DTE, Modem (DCE) detects ring from line.
RTS- Request to Send, DTE requests DCE to become ready to accept the data.
CTS- Clear to Send, DCE acknowledges DTE that I am ready to receive the data. (Response of RTS).
DTR- Data Terminal Ready, DTE is ready to transmit.
DSR- Data Set Ready, DCE is ready to receive.
SGND- Signal Ground

RS232 interface Key Features

Following are the RS232 interface details useful for serial communication.
• Binary 0 range from about +5 to +15 voltage (DC)
• Binary 1 range from about -5 to -15 voltage (DC)
• Start bit - Binary 0
• Data- 5, 6, 7 or 8 bit configurable
• Parity- Odd/even, is not used with 8 bit of data.
• Stop bit: Binary 1, one or two bits

RS 232 technical specifications

The table-1 below mentions RS232 interface technical specifications.

Specifications RS232
Mode of operation Single ended
number of drivers/receivers on one line 1 driver, 1 receiver
maximum cable length 50 feet
maximum data rate 460kbps
max. driver output voltage +/- 25 V
Max. driver current in high impedance state +/-6mA at +/-2V
slew rate(max) 30 V/µS
receiver input voltage range +/-15V
Receiver input sensitivity +/-3V
Driver load impedance 3K to 7K Ohms
Receiver Input Resistance 3K to 7K Ohms

Benefis of RS 232

1. RS-232 is simple to implement, with straightforward wiring and protocol.
2. Despite its age, RS-232 remains widely supported in various industries.
3. RS-232 can support communication over long distances, up to 50 feet, depending on the baud rate and cable quality.
4. It includes control signals such as RTS (Request to Send) and CTS (Clear to Send), which help manage data flow and control communication between devices.

Drawbacks of RS 232

1. RS-232 has relatively low data transfer rates compared to modern communication interfaces, typically 115.2 kbps (maximum). 2. The physical connectors, such as DB25 and DB9, are large and cumbersome compared to more modern alternatives.
3. The wide voltage range (-15V to +15V) can be incompatible with modern low-voltage logic systems, requiring level shifters.
4. RS-232 is designed for point-to-point communication, meaning it can only connect two devices directly.
5. RS-232 can be susceptible to electrical noise, especially over long distances or in electrically noisy environments.

Summary

In summary, while RS-232 is a mature and reliable standard, its limitations in speed, device connectivity, and compatibility with modern systems often make it less suitable for new applications. Nonetheless, its simplicity and widespread support continue to make it relevant in specific niches.

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