The APC Smart-UPS computer interface port is a proprietary port found on APC Smart-UPS 600 VA and above, and Matrix-UPS models, produced from the early 1990s through the 2000s. It supports two operating modes: a basic dumb mode using RS-232 level signals for on-battery and low-battery status, and a smart mode using a full RS-232 serial link at 2400 bps, 8N1, with a proprietary ASCII command protocol. The physical connector on the UPS chassis is a 10-pin RJ50 female receptacle; the cable supplied by APC (e.g. 940-0625A) adapts this to a DB-9 male plug at the PC end, which is what the diagram below depicts. APC designates this the “advanced port”, distinguished from the basic port found on Back-UPS and Smart-UPS v/s models.
9 pin D-SUB male connector at the UPS
| Pin | Signal | Description |
|---|---|---|
| 1 | Shut Down (dumb mode) / RS-232 RX In (smart mode) | Set high for 1-5 sec to activate shutdown. |
| 2 | Line Fail (dumb mode) / RS-232 TX Out (smart mode) | On-battery power (normally low but goes high when the UPS switches to batteries) |
| 3 | Line Fail signal | Mains down (normally low but goes high when line fail) |
| 4,9 | GND | Ground, chassis |
| 5 | Low battery signal | (normally low but goes high when low battery) |
| 6 | Line fail signal | Inverse of pin 2 Line Fail signal |
| 7 | UPS Turn-on/off signal | (on advanced UPSes only) |
| 8 | Unregulated +24 Vdc Out ?? |
Notes
The connector depicted is the DB-9 male plug on the PC end of the APC interface cable (e.g. 940-0625A / AP940-0625A). The UPS chassis uses a 10-pin RJ50 female receptacle. The port is intended for use only with APC-supplied software, cables, and interface accessories.
Open-collector outputs on pins 3, 5, and 6 are rated for ≤25 mA and ≤+40 Vdc; pin 4 (GND/chassis) must be used as the common for these signals. Pin 2 operates at RS-232 levels in both dumb and smart modes. In dumb mode, pin 1 must be held high for 1–6 seconds to trigger a shutdown (timing varies by model: approximately 1 second on some Back-UPS variants, 6 seconds on Smart-UPS). In smart mode, the same pin carries RS-232 RXD data.
Pin 7 (remote on/off) is present on Smart-UPS 600/900/1250/2000 and 450/700/1000/1400/2200/3000 VA models; a momentary high signal turns the UPS on, a momentary low turns it off. Smart-UPS 250/400 VA models have the advanced port but lack pin 7 remote on/off functionality.
Pin 8 provides an unregulated +24 Vdc supply (±10 V tolerance), current-limited to 50 mA, for powering interface accessories.
Signals
- Shut Down / RS-232 RX In — In dumb mode, sustaining a high RS-232 level on this pin triggers UPS shutdown; in smart mode, this pin carries RS-232 serial receive data (2400 bps, 8N1).
- Line Fail / RS-232 TX Out — In dumb mode, transitions from low to high at RS-232 level when the UPS switches to battery power; in smart mode, carries RS-232 serial transmit data.
- Line Fail signal — Open-collector output; goes high when mains supply fails (active-high, normally low).
- GND — Signal and chassis ground; required common for all open-collector outputs.
- Low battery signal — Open-collector output; goes high when battery charge is critically low.
- Line fail signal — Open-collector output; inverse polarity to pin 2 Line Fail signal.
- UPS Turn-on/off signal — Present on advanced-port models only; momentary high turns the UPS on, momentary low turns it off. Function unknown on models without remote on/off support.
- Unregulated +24 Vdc Out — Unregulated DC supply output (nominally +24 V, ±10 V), current-limited to 50 mA; intended to power APC interface accessories.