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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
| 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 rails 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 2.5V power rail.
Voltage VccIO for bank B0 shall span from 2.5 V
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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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Figure 37: example of VCCIO0 assembly not dependent on 2.5 V power rail. The other way is also possible.
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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