RS232 VS DB9: Disadvantages and advantages of RS232 and DB9, Differences between the RS232 and DB9

In RS232, ‘RS’ stands for Recommended Standard. It defines serial communication using DTE and DCE signals. Here, DTE refers to Data Terminal Equipment and DCE refers to Data Communication Equipment. An example of a DTE device is a computer and DCE is a modem. Formally, it is specified as the interface between DTE equipment and DCE equipment using serial binary data exchange.

The DTE (computer) transmits the information serially to the other end equipment DCE (modem). In this case, DTE sends binary data “11011101” to DCE and DCE sends binary data “11010101” to the DTE device. RS232 describes the common voltage levels, electrical standards, operation mode, and a number of bits to be transferred from DTE to DCE. This standard is used for the transmission of information exchange over telephone lines.

The working of RS-232 can be understood by the protocol format. As RS-232 is a point-to-point asynchronous communication protocol, it sends data in a single direction. Here, no clock is required for synchronizing the transmitter and receiver. The data format is initiated with a start bit followed by 7-bit binary data, parity bit, and stop bit which are sent one after another.

The transmission begins by sending a Start bit ‘0’. This is succeeded by 7 bits of ASCII data. The parity bit is appended to this data for the receiver validation. The data sent from the transmitter should match the receiver. Finally, the transmission is halted using a stop bit and it is represented by the binary ‘1’. Generally, 1 or 2 stop bits can be sent. In the above diagram, ASCII character ‘A’ is sent using a serial binary stream of ‘1’s and ‘0’s. While sending data, there should be a certain delay between each bit. This delay is considered as inactive time and the RS232 line is at a negative logic state (-12V).

The term "DB9" refers to a common connector type, one of the D-Subminiature or D-Sub types of connectors.  DB9 has the smallest "footprint" of the D-Subminiature connectors and houses 9 pins (for the male connector) or 9 holes (for the female connector).

DB9 connectors were once very common on PCs and servers.  DB9 connectors are designed to work with the EIA/TIA 232 serial interface standard, which determined the function of all nine pins as a standard so that multiple companies could design them into their products.  DB9 connectors were commonly used for serial peripheral devices like keyboards, mice, joysticks, etc. Also, they are used on DB9 cable assemblies for data connectivity.

Today, the DB9 has mostly been replaced by more modern interfaces such as USB, PS/2, Firewire, and others.  However, there are still many legacy devices that use the DB9 interface for serial communication.

RS232  3D Model

RS232 Symbol

RS232 Footprint

DB9  3D Model

DB9 Symbol

DB9 Footprint

RS232 Features

• Features molded hoods and thumbscrews that enable a snug fit when making connections.

• All nine pins are wired straight through.

DB9 Features

• DB9 protects 9 pin serial connections for data line surge suppression of data terminal, data communications equipment and PCs, printers, modems, and more

• Reversible for use with male or female captive DB9 ports

• Offers protection on all 9 data lines, plus D shell chassis

• Surge suppression utilizing high-speed avalanche diodes divert excess energies on the network to

• Ground

RS232 Advantages

• RS232 interface is supported in many compatible legacy devices due to its simplicity. It is widely used for point-to-point connections between DTE and DCE devices.

• It supports long distances of about 50 feet (for low baud rates) and with error correction capabilities.

• RS232 is immune to noise due to the use of +/-5 Volts or higher for binary logic 0 and logic 1.

• RS232 is a low-cost interface.

• Converters or adaptors are available at cheaper rates for conversion from RS232 to RS485/USB/Ethernet etc.

RS232 Disadvantages

• It is suitable for system-to-system communications. It is not suitable for chip to chip or chip to sensor device communications.

• Supports lower speed for long distances. Higher speed (i.e. 115200 baud) can be achieved for short distances only.

• RS232 interface requires separate transceiver chips which will add cost to the system.

• It is used for single master and single slave configuration and not for single master-multiple slaves mode.

• It is an unbalanced transmission.

DB9 Advantages

DB9 connectors have several advantages. You can easily customize them with 9 individual pins to carry serial data. Although the speed of these connectors is low as compared to other standards like USB, the length of these cables is quite long. For eg, USB has a five-meter length limit, but RS-232, which is the most commonly used standard for serial data doesn’t have a particularly defined length limit. RS-422 has been used at length which is hundreds of meters long with special equipment.

In case you have an old device having DB9 connectors on it, you will find several options for conversions. Converters from other standards like USB, Ethernet, etc also enable you to make use of your device on any computer.

DB9 Disadvantages

As the connectors are large, it becomes difficult to connect and disconnect them in small spaces. The pins of these cables are usually exposed so there are more chances for them to get damaged or break. Although you can mate the connector without any thumbscrew hardware, there are fewer chances that it will hold on to the equipment. On the other hand, if you use thumbscrews, the connector will take a long time to get plugged and unplugged.

And as mentioned before, serial communication is a slow and old way of exchanging data. So the speed is quite slow when there are cables of long length. This also causes breaks in communication and makes the software of PC freeze. Due to such issues, other standards gained more popularity over DB9 cables.

But this in no way means that DB9 connectors aren’t used. If you use right-angle adapters, they can help you solve the tight space issue without causing any damage to the connector. You can attach the connectors with D-Subminiature plug and jack covers which can protect pins from getting damaged when not being used.

Before you make a buy for DB9 connectors, make sure you precisely know what your needs are. If there is a smart alternative for DB9 cables, you can go for that as well!

The serial interface is defined by RS232, which includes things like signal voltage and duration. The 9-pin connector is known as DB9. These connectors are commonly used for RS232 connections, but there is also a 25-pin connector. RS232 is the definition of the serial interface, e.g. the signal voltage and duration. DB9 is the 9-pin connector. RS232 connections are frequently implemented using these connectors, but there is a 25-pin connector also. But of course, you can solder the cable to the devices directly also, without a DB9 or DB25 connector.

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RS232 Datasheet

DB9 Datasheet