4.2.2 Serial Cable for Debugging User-Mode Drivers
Hardware protocol is used by WinDbg and WinDbgRm to communicate with each other across a serial cable. Hardware protocol requires a cable that connects RXD to TXD, TXD to RXD, DTR to DTR, GND to GND, and DSR to DSR. In addition, each side of the cable should connect DTR to DSR and RTS to CTS. The following table lists the pin numbers of these signals for 9-pin and 25-pin connectors.
| Signal | 9-pin Pin # | 25-pin Pin # |
| RXD (Receive Data) | 2 | 3 |
| TXD (Transmit Data) | 3 | 2 |
| DTR (Data Terminal Ready) | 4 | 20 |
| GND (Signal Ground) | 5 | 7 |
| DSR (Data Set Ready) | 6 | 6 |
| RTS (Request to Send) | 7 | 4 |
| CTS (Clear to Send) | 8 | 5 |
The connections are a superset of the connections necessary for a kernel debugging cable. You can use this cable for kernel debugging.