DB 9 Loopback


A DB 9 Loopback is a type of telephone switch used to provide connectivity between two telephones. It is also known as a “loop-around” or “circuit breaker”.

The rs232 loopback plug is a device that allows you to connect two devices together. If one of the devices has an RS-232 port, the other can be plugged into it and then both devices will communicate with each other.

The RS232 connection was designed with 25 pins in mind. A supplementary serial RS232 communication channel was provided in this DB25 connection pin arrangement. There is, however, just one serial communication channel with handshaking. There were just a few computers made that had both RS232 channels accessible. Sun SparcStation 10/20 model and Dec Alpha Multia, for example. When we speak about a loop back connection, we can state that it usually simply consists of a connector. It does not need the use of an external cable. It simply consists of an internal wiring arrangement that allows the same signal to be retransmitted to the sender.

A DTE system may simply connect to this DB9 female connection. When the loop back connection is utilized, the signal is received back by the DTE that sent it out, and it will not be able to tell which source sent it out. It implies that the DTE will be unable to distinguish whether the signal it has received is his own or from another source (DCE).

Now the issue arises: what good is it if it resends the signal back to the sender? The solution is buried in its most basic feature: a Loop back connection is utilized to determine if the system’s serial port is operational or not. After ensuring that the functionalities of your system’s serial port are working properly, you may connect your serial cable. If you wish to double-check your serial cable, just connect the loop back connection at the other end of the cable and repeat the signal verification.


To create a loop back connection, the following pins must be linked, as indicated in the diagram above.

  • Pins 2 (Receive) and 3 (Send) (transmit)
  • Pins 7 (Request to transmit) and 8 (Request to receive) (Clear to send)
  • Pin 1 (Data carrier detect), Pin 6 (Data set ready), and Pin 4 (Data set ready) (Data terminal ready)

The aft view of the female DB-9 connector is shown in the figure below, with red lines and gray dots indicating the linkages to be supplied.


The DB-9 loopback was created specifically for RS 232 data signal testing.

Visit https://electricalfundablog.com/blog/rs-232/618/ to learn more about RS 232.

The DB 9 Loopback is a serial cable that can be used on DB-9 Serial ports. It allows the user to connect two devices together and monitor what one device is sending to the other.

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  • serial loopback pinout
  • rs232 cable
  • serial port
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