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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 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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  control.When S2 is turned on (closed, FX2 PON), the power rails 1.2 V and 2.5 V 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 enables (switches on) power rails 1.2 V and 2.5 V, 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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title Slide switch S2 settings overview (power rails 1.2 V and 2.5 V only)
S2 position Default position Effect on 1.2 V and 2.5 V rails FX2 PON (on, closed)  Power rails 1.2 V and 2.5 V 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 always enabled (PS_EN = 1) PS_EN ≠ FX_PS_EN = 1 or 0

Table 14: Slide switch S2 settings overview (power rails 1.2 V and 2.5 V only).

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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title Table from EZ-USB(R) Technical Reference Manual
Table from EZ-USB(R) Technical Reference Manual (EZ-USB_TRM.pdf) Port D Pin Alternate Function Alternate Function is Selected By... Alternate Function is Described in... PD.7:0 FD[15:8] IFCFG1 = 1 and any WORDWIIDE bit = 1 Slave FIFOs chapter 9 on page 99

Table from EZ-USB(R) Technical Reference Manual (EZ-USB_TRM.pdf).

Signal PS_EN

• Signal PS_EN enables (1) or disables (0) power rails 1.2 V and 2.5 V.
  
  Figure 36: Power rails 1.2 V and 2.5 V could be enabled/disabled by signal PS_EN.

• Power-rail 3.3V is not controlled by signal PS_EN and is unconditionally enabled. 
    
  Figure 37: Power rail 3.3 V could not be enabled/disabled by signal PS_EN..

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).

Figure 37: example of VCCIO0 assembly not dependent on power rail 2.5V. The other way is also possible.

Slide Switch S2 = FX2 PON 

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