Here is a description of the caple needed to connect a Smart-UPS
to a COM-Port of a (IBM-)PC.

Note: I don't take any responsibility for the correctness of this information.
It is provided as is. I provide this information to allow users to manufacture
replacement cables, in case the old one gots lost or damaged.
I took every effort to insure correctness.
Measurements were taken from a cable supplied with an APC Smart-UPS900I which
is controlled by APC PowerChute 4.0 for OS/2.
It can be assumed, that all Smart-UPS use the same configuration.
This may not be true for other UPS lines from APC.

UPS-End:
Male-DB-9 connector , pins being called here U1..U9

COM-End:
Female-DB-9 connector , pins being called here C1..C9

1. Connect C1-C4 (short cut between CD and DTR)
2. Connect C2-U2 (data from UPS into RXD)
3. Connect C3-U1 (data from TXD into UPS)
4. Connect C5-U9 (ground)
No other connections (resistance less than 10 kOhm) have been found.
Connect means : no substantial resistance ( less than 5 Ohm ).

Remarks:

Apparently APC went great lengths avoiding any standards to make money with their cables.
Avoidance of standards in general brings only problems, increases cost to the end user
and may cause hardware damage.
The Smart-UPS is really great , the attitude of APC when developing that cable layout not.

The UPS sends data at 2400 bps , 8N1 in regular intervalls. The cable does not permit
any hardware handshaking (which is bad, because it decreases performance of any software
sitting at the other end)

