The purpose of this document is to provide additional information on the PC-Doctor Serial Port Loopback Adapter.
The serial port loopback adapter is designed to loop incoming data back to the serial port and is necessary to run the Serial Port External Loopback Test in Service Center for Windows, Bootable Diagnostics, and DOS. Attach the serial port loopback adapter to the 9-pin Serial (COM) port on your PC. Your PC may have more than one serial port. The adapter can be seen below: