I replaced my old APC SmartUPS 620 with an updated model. I had lost the serial cable that allows you to communicate with the UPS via a computer for the old unit. The new unit came with the serial cable and for a while I was looking for the correct pin out so I could build a cable myself. So I wanted to get the pin out documented. The cable is a male to female DB9 cable. Well I got my voltmeter and using the continuity setting I mapped the pinout. It would not be difficult to create this cable. Many of the cables DB9 serial cables I had laying around were female to female and it was hard finding a male end. Hopefully this will help others out there that need this cable and don’t want to pay $30 for it.
UPDATE: I have updated the diagram based on the comments I got on this post. Apparently I counted the male pins incorrectly so I made the correction. Thanks for your feedback.

July 3rd, 2009 at 12:52 am
Hi, you have the SmartUPS cable slightly wrong. The picture is correct, but you have counted the pins on the male connector incorrectly. The correct table should be:
Fem Male
2 2
3 1
5 9
Cheers,
November 12th, 2009 at 11:26 pm
Mr Ball (posted on 7/3/2009) is correct you should correct the db9 male side pin numbers. Other wise nice diagram!
Thanks…