What is RS232 protocol?
The RS232 protocol is a popular serial interface used to connect computers to networked devices such as serial servers. We will look at the serial port pins used to implement RS232 and some other reference information about the protocol.
The RS232 protocol transmits wire data using a different signal level than the standard 5V to minimize signal interference. It performs asynchronous transmission at a constant rate that is synchronized with the level of the start pulse signal. A distance of up to 20 meters is the limit for reliable data transmission using the RS232 interface.
What does RS232 stand for?
Data transmission standards are developed by the Electronic Industries Association (EIA). The prefix RS indicates a recommended standard, and all EIA standards begin with these characters. The formal specification of RS232 is that it is an interface for communication between DTE and DCE devices using serial binary data exchange. DTE is the abbreviation of data terminal equipment, while DCE stands for data communications equipment. A basic example of these two devices defines the computer as a DTE device, with the serial server assuming the role of DCE.
Serial communication is achieved by transmitting serial data between the DTE and DCE. For example, a computer (DTE) might send binary data “11011101” serially to a serial server (DCE), and the serial server replies by sending “11010101” back to the DTE device.
The RS232 protocol is used to transfer data between DTE and DCE by specifying the operating mode, electrical standard, number of bits and voltage levels.
Serial server–serial communication equipment
Serial communication devices use 9 or 25-pin D-type connectors for cabling. They are usually designated DB-9 or DB-25, with the number distinguishing the pin count. Various manufacturer’s names may replace DB in the specification. A plug consists of a socket and pins, each of which is numbered and labeled. The serial pinout diagram is shown below.
The RS232 protocol uses a 9-pin serial port, which can have a male or female connector. The latest version of this protocol is called RS232C.
RS232C retains the functionality of RS232 but uses 25-pin serial pins instead of 9-pin. Whether using the DB9 serial pinout or the 25-pin connection, only three pins are needed to connect to the end device.
COM port pinout and configuration
RS232 uses the serial pin assignments of DB9 or DB25 to manage the communication flow between the DTE and DCE. These D-sub connectors can be terminated with RS232 female pins or DB25 or DB9 female pins. Each pin in the 9 or 25 serial connector pinout has its own unique function. You can also learn about the RS485 pinout.
Function Description:
In addition to defining electrical characteristics, RS232 also specifies signals for use on serial cable pinouts and serial ports. Included in these specifications are familiar items such as timing signals and ground.
The following is a list of signals used in the RS232 COM port pinout:
Protective Ground: This signal is connected to the chassis ground of the metal connector.
Common Ground: The zero reference voltage level for all control signals.
TxD (transmission pin): transmits data from DTE to DCE.
RxD (receive pin): Send data from DCE to DTE.
DTR (data terminal ready): DTE is ready to accept requests.
DCD (Data Carrier Detection): DCE accepts the carrier from a DTE located at a remote location.
DSR (Data Set Ready): DCE is ready to send and receive information.
RI (Ring Indicator): Detects incoming call ringtones on the telephone line.
RTS (Request to Send): DCE’s DTE call to send data.
RTR (Ready to Receive): The DTE is ready to receive data from the DCE.
CTS (clear to send): DCE is in ready state and can accept data from DTE.
These signals are the primary RS232 signals, but the protocol allows secondary signals as well. They include auxiliary DTE, RTS, DCD, TxD and RxD. Auxiliary signals are used to optionally connect DTE and DCE equipment.
RS232 air serial port networking converter connection
The serial port server enables serial communication between DTE and DCE devices. The RS232 air serial port networking converter pinout connects the Tx pin of the male connector to the Rx pin of the RS232 female connector and the pin of the Rx male connector to the Tx pin of the female connector.
Using the RS232 protocol, you can use a zero-serial cable to connect two computers without a serial networking converter. This highlights one of the original uses of the RS232 protocol, which was developed to allow teletype machines to communicate with each other via their serial port servers.
straight-through cable
Another type of RS-232 cable is a straight-through cable. It is a one-to-one connector that transmits the pins of one device, which connect to the transmit pins of another device, and the receiver pins of one device, which connect to the receiver pins of another device.
The reason is that RS232 signals travel longer distances. Moreover, it has better noise immunity. It has proven to be compatible between different manufacturers of connected computers and serial servers.