9 pin D-SUB male connector
The Megatech M2501 and M2603 are proprietary cables for connecting Megatech UPS units to a PC serial port via a DE-9 (9-pin D-sub) connector. The M2501 (Type I) carries the Megatec/Q1 intelligent serial protocol — a widely adopted late-1990s Taiwanese standard running at 2400 bps, 8N1 — allowing bidirectional ASCII communication for status queries and shutdown commands. The M2603 (Type II) is a simpler contact-closure cable that signals mains failure and low battery via voltage levels on dedicated pins, with pin 7 repurposed as the ground return for the shutdown line.
| PC Pin name | PC Pin | Direction | UPS Pin | UPS Pin name | Description |
|---|---|---|---|---|---|
| NC | 1 | - | 1 | NC | |
| AC Power Failure | 2 | IN | 2 | AC Power Failure | Active negative level (negative impulse indicates a power failure) |
| NC | 3 | - | 3 | NC | |
| Common Ground of Pin 2, 5, 6 | 4 | 4 | Common Ground of Pin 2, 5, 6 | ||
| UPS Battery Low | 5 | IN | 5 | UPS Battery Low | Active negative level (negative impulse indicates a battery low power level) |
| Turn Off UPS | 6 | IN | 6 | Turn Off UPS | Active positive level (positive impulse sent by PC shuts down the UPS) |
| NC / GND for pin 6 | 7 | - | 7 | NC / GND for pin 6 | NC in Type I cable. GND for pin 6 in Type II cable. |
| NC | 8 | - | 8 | NC | |
| NC | 9 | - | 9 | NC |
Notes
The two cable types differ at pin 7 only: in the Type I (M2501) cable pin 7 is not connected, whereas in the Type II (M2603) cable pin 7 serves as the ground return for the shutdown signal on pin 6. The DE-9 connector is male on the cable end. Status signals on pins 2 and 5 are active-negative (a negative voltage impulse indicates the condition); the shutdown signal on pin 6 is active-positive (a positive impulse from the PC initiates UPS shutdown). The Type I intelligent protocol uses 2400 bps, 8 data bits, 1 stop bit, no parity, on a separate set of UPS pins not exposed through this cable’s contact-closure mapping.
Signals
- NC — no connection; pin is unused in both cable types
- AC Power Failure — active negative level; a negative impulse on this line indicates a mains power failure
- Common Ground of Pin 2, 5, 6 — common ground reference shared by the status and shutdown signal lines
- UPS Battery Low — active negative level; a negative impulse indicates the battery has reached a low charge level
- Turn Off UPS — active positive level; a positive impulse sent by the PC triggers UPS shutdown
- NC / GND for pin 6 — not connected in Type I (M2501); acts as the ground return for the shutdown line (pin 6) in Type II (M2603)