22 pin MOLEX 39-29-9222 connector at the motherboard.
The WTX P2 connector is the required secondary power connector defined in Intel’s WTX Power Supply Design Guidelines (Version 1.0, February 1999) for mid-range workstations based on the WTX form factor, introduced in September 1998. It is a 22-pin (2×11) Molex Mini-Fit Jr. housing carrying the +12V_IO rail, the −12 V rail, remote sense lines for the +5 V and +3.3 V rails, and all system control signals including PS-ON#, SLEEP#, PS-OK, fan control, fan monitoring, and an optional I2C bus. P2 must be used together with the primary P1 connector; without it, the power supply control and supervisory functions are absent. The board-side housing is Molex 39-29-9222 and the cable-side housing is Molex 39-01-2220.
| Pin | Name | Color | Description |
|---|---|---|---|
| 1 | 5Vsense | red | Sense +5 VDC |
| 2 | 3.3Vsense | orange | Sense +3.3 VDC |
| 3 | res | reserved | |
| 4 | com | black | Ground |
| 5 | com | black | Ground |
| 6 | 12Vio | yellow | +12 VDC (I/O) |
| 7 | -12V | blue | -12 VDC |
| 8 | I2C clk | I2C Clock (optional?) | |
| 9 | FanC | purple | Fan Control |
| 10 | PS-OK | grey | PoweSupply Ok |
| 11 | res | reserved | |
| 12 | 5Vsensertn | black | Ground Sense +5 VDC |
| 13 | 3.3Vsensertn | black | Ground Sense +3.3 VDC |
| 14 | res | reserved | |
| 15 | com | black | Ground |
| 16 | 12Vio | yellow | +12 VDC (I/O) |
| 17 | 12Vio | yellow | +12 VDC (I/O) |
| 18 | sleep | white | Sleep |
| 19 | I2C data | I2C Data (Optional?) | |
| 20 | FanM | brown | Fan Monitor |
| 21 | PS-on | green | PowerSupply On |
| 22 | res | reserved |
Notes
The P2 connector uses the Molex Mini-Fit Jr. family and is keyed to prevent mating with P1 or P3; the housings have different pin counts (22 vs 24 vs 8) so accidental cross-mating is mechanically prevented. The +12V_IO rail (pins 6, 16, 17) must remain within ±5% (11.40–12.60 V) under load; maximum ripple is 120 mVpp. The −12 V rail (pin 7) is regulated to ±10% (−10.80 to −13.20 V). Remote sense lines on pins 1, 2, 12, and 13 allow the PSU to compensate for voltage drop in the cable between the PSU and the P1 connector; these are distinct from the power pins on P1. In dual-fan PSU units, the SLEEP# signal (pin 18) also causes one fan to be switched off when the system enters a low-power sleep state.
Pins 11 and 22 are labelled “res” (reserved) on this page; in the WTX Power Supply Design Guidelines they are provisioned for an IEEE 1394 (FireWire) auxiliary power pair, but this function was not implemented on the Intel Pentium III/840 Development Kit board (where they appear as no-connection).
Signals
- 5Vsense — Remote sense input for the +5 V rail; the PSU uses this to regulate output voltage at the motherboard rather than at the cable end.
- 3.3Vsense — Remote sense input for the +3.3 V rail; paired with 3.3Vsensertn on pin 13.
- res (pins 3, 11, 14, 22) — Reserved; pins 11 and 22 are provisioned in the specification for an IEEE 1394 auxiliary power pair but are not connected on known implementations.
- com (pins 4, 5, 15) — Ground return for the P2 connector.
- 12Vio (pins 6, 16, 17) — +12 V I/O rail supplying the motherboard I/O subsystem; three pins share the current to stay within the 240 VA IEC 60950 per-output limit.
- -12V — Negative 12 V rail, regulated to ±10%; typically used for legacy RS-232 level shifters.
- I2C clk (pin 8) — Optional I2C clock line for PSU management; not populated on the Pentium III/840 Development Kit.
- FanC (pin 9) — Active-low fan control override signal; when asserted, forces PSU fans to run at maximum speed regardless of thermal conditions.
- PS-OK (pin 10) — Power-good signal, TTL-compatible +5 V output from the PSU pulled up via a 5.1 kΩ resistor; logic high (2.4–5 V) indicates all rails are within regulation limits. POK assertion delay is 100–500 ms after rails stabilise.
- 5Vsensertn (pin 12) — Remote sense return for the +5 V rail; completes the Kelvin sense loop with pin 1.
- 3.3Vsensertn (pin 13) — Remote sense return for the +3.3 V rail; completes the Kelvin sense loop with pin 2.
- sleep (pin 18) — SLEEP# signal, active-low, pulled up to +3.3V_AUX via 10 kΩ; asserted by the motherboard to disable secondary CPU power rails and reduce PSU output in suspend states. In dual-fan units, also shuts off one fan.
- I2C data (pin 19) — Optional I2C data line for PSU management; not populated on the Pentium III/840 Development Kit.
- FanM (pin 20) — Fan monitor tachometer, open-collector output generating 2 pulses per fan revolution; allows the system to detect fan failure.
- PS-on (pin 21) — PS-ON# signal, active-low, pulled up to +3.3V_AUX via 10 kΩ; held low by the motherboard to turn on the PSU main outputs (Vil = 0.1–0.8 V, Vih = 2.0–3.47 V).
References
- WTX Power Supply Design Guidelines, Version 1.0 — Intel Corporation, February 1999
- Intel Pentium III Processor/840 Development Kit Manual (Order Number 273333-003) — Intel Corporation, April 2001