I lost the diagram. I went out and took apart the adapter I made and took pics. Not sure how to show them here. Basically- RJ22 plug with the tab up, wires left. From the bottom: black, red, green, yellow ( I used a length of old flat phone wire). On the DB9 side: DB9 female 5pins facing up and to the left: top is yellow, middle is red, bottom is black. green is unused. Then use an off the shelf USB to 9 pin serial adapter and mine just worked. DTV box is D12-300. I am not responsible if it doesnt work or smokes your box...
Edited to add: RJ22 is the smaller RJ11 style plug that plugged the handset to the base in and old school wired phone. Not the same size as RJ11 from base to the wall.
