APC Smart UPS DB9 Cable Pinout

APC Part 940-0024C, 940-0024B, 940-0024D or 940-1524 (black cable) are cables compatible with the non-standard APC UPS serial port. The wiring of the cables is as follows:

UPS Signal	DB-9 Male (UPS)	DB-9 Female (PC)	PC Signal Name
TX / AC Fail	2	2	Rx, Received Data
RX / Shutdown	1	3	Tx, Transmitted Data
Common	9	5	GND

A possible schematic could be:

       9pin D-SUB male
    1        PC         5
     +-----------------+
      \ +  +  +  +  +------+
       \| +| +  +  + /     |
        |--|--------+      |
      6 |  |TX        9    |
        |  |               |
        |  |               |
     RX |  +-----+         |
        +-----+  |         |
              |  |         |
    5         |  |      1  | GND
     +--------|--|-----+   |
      \ +  +  +  +  + /    |
       \  +  +  +  + /     |
        +-|---------+      |
      9   |           6    |
          |                |
          +----------------+
       9pin D-SUB female
             UPS

Or, an illustration: