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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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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.
Scroll pdf title title 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.
The power-rail 3.3 V though is out of the control of the USB-microcontroller and is supplied down-converting the power supply 5 V provided by either the USB-bus or the B2B receptacle connector. In this case, signals that are applied to the 3.3 V I/O banks do not need to be disconnected when power-rails are disabled by the USB microcontroller.Scroll pdf title title Power rail 3.3V 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 1.2 V to 3.3 V. VccIO can be supplied either externally or internally to the micromodule.
| Warning |
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| 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). |
Externally Supplied VCCIO
VccIO can be externally supplied over the B2B connector J4. If bank B0 is not used, then VccIO can be left open.
Internally Supplied VCCIO
If VccIO is not externally supplied, it can be internally supplied by one of the internal power rails of 2.5 V and 3.3 V. This is possible by short-circuiting one of the two pad pairs placed on the right of connector J4 at the top right corner of the bottom side of the micromodule.
Two suitable ways of shirt-circuiting the paid pair are by means of a zero-ohm 0603 (1608 metric) chip resistor or a solder blob.
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- Dynamic full power operation (PS_EN = 1): when the EZ-USB FX2LP USB FX2 microcontroller sets signal PS_EN = FX2_PS_EN = 1, power rails 1.2 V and 2.5 V are enabled.
This setting can be useful for . - Dynamic low power operation (PS_EN = 0): when the EZ-USB FX2LP USB FX2 microcontroller resets signal PS_EN = FX2_PS_EN = 0, the following components are switched off:
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Full power operation (PS_EN = 1): when slide switch S3 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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Summary table
The table below summarizes all switching options implied by slide switch S3 and firmware signal FX2_PS_EN (under the standard assembly option).
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(1) R102 populated / R103 unpopulated (2) R102 unpopulated / R103 populated |
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