connector or cable wiring APC part # 940-0119A
9 pin D-SUB male connector to the PC
9 pin D-SUB male connector to the UPS
The APC cable 940-0119A is a simple-signalling (dumb) serial cable used with older Back-UPS ES and Back-UPS Office models. It carries no serial protocol; instead, it uses RS-232 handshaking lines to convey on-battery and low-battery status and to accept a shutdown command from the host. APC Application Note #12 (2004) defines this as a Basic Port design: open-collector outputs on the UPS side signal events directly to the PC via discrete voltage transitions. The cable is a proprietary APC part and is not interchangeable with standard straight-through or null-modem serial cables.
| Computer (DB9-M) | Via | Signal |
|---|---|---|
| DSR 4, DTR 6 | diode + resistor | Kill power |
| DCD 1, RxD 2 | direct | Low battery |
| RTS 7 | two resistors | status drive |
| RI 8, CTS 9 | direct | On battery |
| GND 5 | direct | Ground |
| TxD 3 | — | not connected |
Notes
The cable is a straight-through serial cable with no identification on the plugs. The UPS end is a DB-9 female; the PC end is a DB-9 male. Pin 3 (TxD) at the computer end is not connected (nc). The shutdown signal is applied by the host driving DTR (pin 6) and DSR (pin 4) high through a diode-resistor network; Back-UPS models respond after approximately 1 second of sustained high input. The on-battery and low-battery signals are open-collector outputs from the UPS; a resistor voltage-divider network on pins 7, 8 and 2 converts the UPS internal signals to RS-232-level transitions that the host reads as RI and RxD/DCD respectively. No +24 V supply or remote on/off line is present — this is a Basic Port cable without advanced features.
Signals
- DSR (PC pin 4) — shutdown input path; combined with DTR via diode into UPS kill-power circuit
- DTR (PC pin 6) — shutdown input path; drives UPS shutdown via diode-resistor network (high level for ~1 s triggers shutdown)
- DCD (PC pin 1) — low-battery output; tied to RxD (pin 2) at UPS side
- RxD (PC pin 2) — low-battery output; UPS open-collector output signals low-battery condition
- RTS (PC pin 7) — provides bias current through resistor network for on-battery and low-battery signal conditioning
- RI (PC pin 8) — on-battery output; tied to CTS (pin 9) at UPS side; goes high when UPS is running on battery
- CTS (PC pin 9) — on-battery output; tied to RI (pin 8) at UPS side
- GND (PC pin 5) — signal ground; connected straight through to UPS pin 5
- TxD (PC pin 3) — not connected