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Figure 34: Slide switch S1B schematic.


Figure 35: When slide switch S1B = FX2 PON, signal PS_EN is set to signal FX2_PS_EN driven by the EZ-USB FX2LP USB FX2 microcontroller under user control.

When S1B is turned on off (open) (FX2 PON position), the 1.2 V, 1.5 V and 2.5 V power rails are controlled by the USB (EZ-USB FX2LP USB FX2) microcontroller. At start-up, the USB microcontroller switches off the 1.2 V, 1.5 V and 2.5 V power rails and starts up the module in low-power mode. After enumeration, the USB microcontroller firmware switches the 1.2 V and 2.5 V power rails on, if enough current is available from the USB bus.

When S1B is turned off on (closed) (PON position), the 1.2 V, 1.5 V and 2.5 V power rails are always enabled.

S1B position	Default position	Effect on 1.2V2 V, 1.5V 5 V and  2.5V 5 V rails
FX2 PON (off)		1.2 V and 2.5 V rails controlled by USB FX2 microcontroller (signal FX2_PS_EN) PS_EN = FX2_PS_EN = 1 or 0
PON (on)		1.2 V and 2.5 V rails always enabled (PS_EN = 1) PS_EN ≠ FX_PS_EN = 1 or 0

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