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Scroll pdf title
title Slide switch S2 (angle view).

Scroll pdf title
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

 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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Scroll pdf title
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

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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

Signal PS_EN

• Signal PS_EN enables (1) or disables (0) power rails 1.2 V and 2.5 V.

  
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  Figure 36:

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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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  Figure 37:

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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

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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Figure 37:

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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 

When slide switch S2 is in the left position ( = FX2 PON : 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 control (IOD and OED of fw.c).

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1. Dynamic full power operation (PS_EN = 1): when the EZ-USB FX2LP USB FX2 microcontroller sets signal PS_EN = FX2_PS_EN = high, power rails 1.2 V and 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:

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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.Image Removed Image Removed
Figure 39:

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title S2 on position PON (PS_

EN ≠

EN ≠ FX2_PS_EN = x;

 

PS_EN = high )

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Summary table

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

Table 40: Slide switch S2 settings overview ( 1.2 V , 2.5 V, VCCIO0).

 Alternate Assembly Options for Slide Switch S2

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Assembly option when resistor R17 not populated and R19 populated is equivalent to slide switch S2 permanently set to PON.Image Removed
Figure 41: assembly

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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.Image Removed
Figure 42:

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