24 pin SUN aux power connector at the motherboard.
The Sun Motherboard Aux Power 24-pin connector is a proprietary power interface used on Sun Microsystems SPARCengine Ultra AXmp multi-processor workstation motherboards, dating from approximately 1998 to 2001. Unlike contemporary ATX connectors, it carries remote voltage-sensing lines (PWR_SENSE_3.3V, PWR_SENSE_5V, PWR_SENSE_GND) that allow the power supply to compensate for resistive voltage drop along the DC power cables, ensuring tighter regulation at the board. The connector supplies the standard workstation DC rails (+3.3V, +5V, +12V, −12V) across 24 pins and is not electrically or mechanically interchangeable with the 20-pin ATX connector used on the related single-processor SPARCengine Ultra AXi board.
| Pin | Name |
|---|---|
| 1 | +3.3V |
| 2 | GND |
| 3 | +3.3V |
| 4 | GND |
| 5 | +3.3V |
| 6 | GND |
| 7 | +3.3V |
| 8 | GND |
| 9 | PWR_SENSE_3.3V |
| 10 | GND |
| 11 | PWR_SENSE_GND |
| 12 | +12V |
| 13 | +5V |
| 14 | GND |
| 15 | +5V |
| 16 | GND |
| 17 | +5V |
| 18 | GND |
| 19 | +5V |
| 20 | GND |
| 21 | PWR_SENSE_5V |
| 22 | GND |
| 23 | PWR_SENSE_GND |
| 24 | -12V |
Notes
This connector is specific to the SPARCengine Ultra AXmp (multi-processor) platform and should not be confused with the standard ATX 20-pin connector (Molex 39-29-9202, J1901) used on the single-processor SPARCengine Ultra AXi. The 24-pin housing is proprietary; standard ATX power supplies cannot be connected directly. Multiple ground pins are distributed across the connector to reduce impedance on the high-current +3.3V and +5V rails.
Signals
- +3.3V — 3.3 V DC supply rail; carried on four pins (1, 3, 5, 7) to distribute current load
- +5V — 5 V DC supply rail; carried on four pins (13, 15, 17, 19) for current distribution
- +12V — 12 V DC supply rail for drive motors and other high-voltage logic
- -12V — −12 V DC rail for legacy RS-232 signalling and analogue circuitry
- GND — DC return (ground); distributed across multiple pins to minimise resistive drop
- PWR_SENSE_3.3V — remote sensing input enabling the power supply to measure the 3.3 V rail voltage at the board and compensate for cable drop
- PWR_SENSE_5V — remote sensing input enabling the power supply to measure the 5 V rail voltage at the board and compensate for cable drop
- PWR_SENSE_GND — remote sensing ground reference (pins 11 and 23); paired with the voltage-sense lines to complete the Kelvin measurement circuit
References
- SPARCengine Ultra AXi OEM Technical Manual (Part No. 805-3158-03, May 1999) — Appendix A, TABLE A-12: ATX Power Connector J1901
- Sun Ultra 5 Service Manual (Part No. 805-7763-12) — TABLE 4-2: Power Supply Connector J17 Pin Assignments
- SUN SPARCengine Ultra AXmp OEM Technical Manual (Sun Microsystems, c. 1998–2001)