If you have a BackUPS CS, you are probably either using it with the USB cable that is supplied or with the 940-0128A supplied by APC, which permits running the UPS in dumb mode. By building your own cable, you can now run the BackUPS CS models (and perhaps also the ES models) using smart signalling and have all the same information that is available as running it in USB mode.
The jack in the UPS may be easily use a 8 pin RJ45 connector. It is easy to construct the cable by cutting off one end of a standard RJ45-8 ethernet cable and wiring the other end (four wires) into a standard DB9F female serial port connector.
| PC Signal | PC pin | UPS Pin | UPS signal |
|---|---|---|---|
| RxD | 2 | 2 | TxD |
| TxD | 3 | 8 | RxD |
| GND | 5 | 7 | Ground |
| FG | Shield | 4 | Frame Ground |
Though these UPSes are USB UPSes, APC supplies a serial cable (typically with a green DB9 F connector) that has 940-0128A stamped into one side of the plastic serial port connector.
Here is suggested scheme of original 940-0128A cable
APC Part# - 940-0128A
computer --------- Inside the Connector--------- UPS
DB9-F | | RJ50
pin - signal | | Pin - Color
| |
4 DSR ->|---+ |
| | diode resistor |
6 DTR ->|---+---->|------///-----o kill power | 8 Orange
| |
1 DCD <-|----+ |
| | |
2 RxD <-|----+----------------+--o low battery| 3 Brown
| | |
7 RTS ->|-------------+--///--+ |
| | |
| +--///--+ |
| | |
8 RI <-|----+----------------+--o on battery | 2 Black
| | |
9 CTS <-|----+ |
| signal |
5 GND --|------------------------o ground | 7 Red
| |
3 TxD | |
| chassis |
Chassis/GND |------------------------o ground | 4 Black
| |
| Not connected | 1, 5, 6, 9, 10
--------------------------------------
----------------------------------------------------
UPS RJ50
Pin 1 - USB +5V
Pin2 - On Battery
Pin3 - LoBatt (NOT)
Pin4,7 - GND
Pin8 - Shutdown
Pin9 - USB D-
Pin10- USB D+
For making DYI USB cable simply cut USB cable and connect Red wire to Pin1 of RJ50, Black to pin 7, White to pin 9 and Green to pin 10.
Another cable scheme
correct
incorrect