# Serial port loop back plug

(Applicable to BurnInTest Pro version only)

You can purchase high quality molded loop back plugs from PassMark or you can make your own. A loop back plug is a small connector that plugs into the serial port on your computer in order to loop the data output line into the data input line. It also sets a few control lines to trick the computer into thinking that an external device is connected to the port. You'll find below the instructions for making your own serial port loop back plug. These plugs are designed to be plugged into the small 9 pin serial ports on your computer. In conjunction with software such as BurnInTest they allow the testing of the port.

Warning: This is the pin outs of the plug which we have made and successfully tested with our own software on our own PC's. You use this information at your own risk! It's easy to make a mistake and we take no responsibility for the potentially serious consequences.

The serial port on IBM compatible PC's conform to the RS232 electrical standard and use a male DB-9 connector. (older PC's may use a DB-25 in which case a converter will be required). The DB-9 connector as the following 9 pins.

DB9 Pin | EIA Description | Description
1 | DCD | Data carrier detect
2 | RXD | Receive data
3 | TXD | Transmit data
4 | DTR | Data terminal ready
5 | GND | Signal ground
6 | DSR | Data set ready
7 | RTS | Request to send
8 | CTS | Clear to send
9 | RI | Ring Indicator

To make the loop back plug the following pins need to be connected together

- Receive and transmit (2 & 3)
- Request to send and Clear to send (7 & 8)
- Data carrier detect, Data set ready and Data terminal ready (1, 6 & 4)

This diagram shows the connections that need to be made. It's the rear view of the female DB-9 connector that's required for the plug. The red lines and gray dots show the connections that need to be made on the back of the plug.

Female DB-9 connector - Rear view