DB9 Connector

What is DB9 Connector?

DB9 is a D-type data interface connector, with 9 pins (for the male connector) or 9 holes (for the female connector). It is commonly used for serial communications, such as RS-232 or RS-422, and is also known as a DE-9 connector or a serial port connector. DB9 connectors are commonly used to connect devices such as computers, printers, and modems. The pins are arranged in a D-shaped shell and are typically labeled with numbers or letters to indicate their function. The DB9 connector is a legacy connector that is being replaced by newer, more versatile connectors such as USB and Ethernet.

DB9 Connector Pinout

db9 connector datasheet
db9 male connector pinout and db9 female connector pinout
db9 male and female connector pinout
  • 1 DCD carrier detect

When the data carrier is detected, the Modem sends it to the DTE, indicating that the carrier signal of the other party has been detected.

  • 2 RXD Receive data
  • 3 TXD sends data
  • 4 DTR data terminals ready

After the DTE equipment is powered on, and can correctly realize the function of communication, it sends a DTR signal to the DCE, indicating that the data terminal has been prepared and can communicate.

  • 5 SG Signal ground
  • 6 DSR data ready

The data device is a device for DCE communication. For example, after the Modem is powered on and can perform the communication function normally, it sends a DSR signal to the DTE, indicating that the Modem is ready. These two are ready to signal, and in the process of communication, they should be tested first to understand the state of each other to establish communication reliably. However, if the other party of the communication does not require testing, this signal may not be issued.

  • 7 RTS request to send

When DTE has data and needs to transmit communication to the remote DTE, the DTE will send a call to the remote Modem according to the provided destination telephone code when it detects that the DSR is valid, that is when the Modem receives the signal. The remote RST receives this call, first emits a 2000Hz blast to turn off the telephone line echo canceller, and then sends an answer carrier signal. The local Modem receives the carrier signal and confirms that it has obtained the consent of the two parties. It sends the original carrier signal to the remote Modem, indicating to the other party that it is an available Modem. At the same time, it uses the 8th lead of RS232C to send the data carrier signal DCD, indicating to DTE that it has been A valid reply carrier signal is detected.

  • 8 CTS Clear to Send

Whenever a Modem recognizes that the other Modem is ready to run and receive, it will use the CTS signal to notify its own DTE, indicating that the communication channel is ready for data transmission, allowing DTE to send data. At this point, the communication link is established and communication begins.
In half-duplex communication, the CTS is the answer to the RTS signal of the DTE, so the DTE starts to transmit data. In full-duplex communication, the CTS is generally maintained for a long time, while the RTS is not required to be maintained for a long time. After the communication link is established, it can be lowered.

  • 9 RI Ringing Alert

If the Modem can answer automatically, when the other party’s communication call comes, the Modem sends a signal to the DTE with the lead to indicate the call. After the ringing of the telephone call, the Modem will automatically answer the other party immediately under the condition that the DTE is ready for communication (that is, the DTE is valid).

db9 connector dimensions

db9 female and male connector dimensions

DB9 connectors are used for

The application fields of DB9 connectors mainly involve three aspects: communication, network, and video. The details are as follows:

  1. Communication port

One of the most widespread uses of D-sub is for RS-232 serial communications, and while this standard is not currently mandated, it is the industry default. RS-232 devices originally used DB25, but for many applications the less common signals were omitted, allowing the use of DB9 female and male connectors. Many uninterruptible power supply units are equipped with DB9 connectors to signal the connected computer via the RS-232 interface. These typically don’t send data serially to the computer but use handshake control lines to indicate low battery, power failure, or other conditions. But this use among DB connector manufacturers is not standardized and may require special cables.

  1. Network port

DE9 connectors are used in some token ring networks as well as other computer networks. DB9 connectors are typically used for CAN: DB9 female connectors are on the bus, and DB9 male connectors are on the device.

  1. Computer video output, game controller port

db9 connector vs rs232

RS232’s standard name is DB25, DB9 is the next generation interface of DB25 and can be converted to each other

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