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TE0320 is provided with a slide switch S2.
Slide switch S2 conditions the value of signal PS_EN.
In this way, S2 conditionally/unconditionally enables the 1.2 V and 2.5 V power rails.Image Removed
Figure 33:

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title Slide switch S2 (angle view).
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title Slide switch S2 schematic
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title When slide switch S2 = FX2 PON, signal PS_EN is set to signal FX2_PS_EN driven by the EZ-USB FX2LP USB FX2 microcontroller under user control
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 When S2 is turned on (closed, FX2 PON), the power rails 1.2 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 and 2.5 V power rails and starts up the module in low-power mode. After enumeration, the USB microcontroller firmware switches the 1enables (switches on) power rails 1.2 V and 2.5 V power rails on, if enough current is available from the USB bus. 

When S2 is turned off (open, PON), the 1.2 V and 2.5 V power rails are always enabled (switched on).

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Power rails 1.2 V and 2.5 V

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controlled by USB FX2 microcontroller (signal FX2_PS_EN) PS_EN = FX2_PS_EN = 1 or 0 PON (off, open) Power rails 1.2 V and 2.5 V

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Signal FX2_PS_EN

To command signal FX2_PS_EN, read the reference firmware code.
IOD = 0x03; // Enable PS_EN and disable PROG_B
OED = 0x03; // Configure PS_EN and PROG as outputs

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• .

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  title Power rails 1.2 V and 2.5 V could be enabled/disabled by signal PS_EN
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• Power-rail 3.3V is not controlled by signal PS_EN and is unconditionally enabled. 

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  title Power rail 3.3 V could not be enabled/disabled by signal PS_EN
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VCCIO0 assembly options

According to the corresponding assembly option, power rail VCCCIO0 can depend or not on the power rail 2.5V.

Voltage VccIO for bank B0 shall span from 2.5 V to 3.3 V. VccIO can be supplied either externally or internally to the micromodule.

Warning
Spartan-3 I/Os are not 5 V tolerant. Applying more than the recommended operating voltages at any pin, results in a damaged FPGA (see Xilinx Answer AR#19146).

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title example of VCCIO0 assembly not dependent on power rail 2.5V. The other way is also possible
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Slide Switch S2 = FX2 PON 

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When slide switch S2 is in the left position ( = FX2 PON

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: power rails conditionally on depending on signal FX2_PS_EN), signal PS_EN is set to signal FX2_PS_EN (PS_EN = FX2_PS_EN) driven by the EZ-USB FX2LP USB FX2 microcontroller under user

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control (IOD and OED of fw.c).

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title S2 on position FX2 PON (PS_EN = FX2_PS_EN = 1 or 0 )
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1. Dynamic full power operation (PS_EN = 1): when the EZ-USB FX2LP USB FX2 microcontroller

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1. sets signal PS_EN = FX2_PS_EN

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1. = high, power rails 1.2

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1. V and

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Power-rail 3.3V is not controlled by signal PS_EN and is unconditionally enabled. 
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Figure 38: Power rails 3.3V could not be enabled/disabled by signal PS_EN.

1. 2.5 V are enabled.
   This setting can be useful for .
2. Dynamic low power operation (PS_EN = 0): when the EZ-USB FX2LP USB FX2 microcontroller resets signal PS_EN = FX2_PS_EN = low, the following components are switched off:

• • FPGA core logic (1.2V)
  • DDR SDRAM (2.5V)
  • FPGA bank 3 (2.5V)
  • VREF (2.5V)
  • VCCCIO0 (2.5V) FPGA bank 0 (if R131+R132- assembly)

Slide Switch S2 = PON 

Full power operation (PS_EN = 1): when slide switch S2 is in the right position (PON = power rails unconditionally on), signal PS_EN is set to power rail 3.3V. Thus power rails 1.2 V and 2.5 V are unconditionally enabled.

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title S2 on position PON (PS_EN ≠ FX2_PS_EN = x; PS_EN = high )
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Summary table

The table below Table 14 summarizes all switching options implied by slide switch S2 and firmware signal FX2_PS_EN (under the standard assembly option).

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Table 14: Slide switch S2 settings overview ( 1.2V , 2.5V, VCCIO0).

 Alternate Assembly Options for Slide Switch S2

Slide switch S2 can be replaced by one resistors in the following cases:

• cost sensitive applications
• applications where just one position of S2 is required
• application where switching of S2 is not allowed.

Assembly option when resistor R17 not populated and R19 populated is equivalent to slide switch S2 permanently set to PON.

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title Assembly option: S2 = PON
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Assembly option when resistor R17 populated and R19 not populated is equivalent to slide switch S2 permanently set to FX2 PON.

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title Assembly option: S2 = FX2 PON
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