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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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Table from EZ-USB(R) Technical Reference Manual (EZ-USB_TRM.pdf)
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Signal PS_EN enables (1) or disables (0) power rails 1.2 V and 2.5 V.
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Power-rail 3.3V is not controlled by signal PS_EN and is unconditionally enabled.
Figure 37:
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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 |
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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:
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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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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.
Figure 39:
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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).
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(1) R131 populated / R132 unpopulated (2) R131 unpopulated / R132 populated |
Table 40: Slide switch S2 settings overview ( 1.2 V , 2.5 V, VCCIO0).
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Assembly option when resistor R17 not populated and R19 populated is equivalent to slide switch S2 permanently set to PON.
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.
Figure 42:
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Any other assembly options of R17 and R19 are not allowed. |