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.

Figure 33: Slide switch S2 (angle view).

Figure 34: Slide switch S2 schematic.


Figure 35: 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).

	When S2 is turned on (FX2 PON), make sure that no signals are applied to the input pins when power-rails are disabled by the USB microcontroller (at start-up).

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

 

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 

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).

Figure 38: S2 on position FX2 PON (PS_EN = FX2_PS_EN = 1 or 0 ).  

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:

• • FPGA core logic (1.2V)
  • DDR SDRAM (2.5V)
  • FPGA bank 3 (2.5V)
  • VREF (2.5V)
  • VCCCIO0 (2.5V) FPGA bank 0 (if R131+R132- assembly)

Slide Switch S2 = PON 

Summary table

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

⁽¹⁾ R131 populated / R132 unpopulated

⁽²⁾ R131 unpopulated / R132 populated

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

 Alternate Assembly Options for Slide Switch S2

Slide switch S2 can be replaced by one resistors in the following cases:

• cost sensitive applications
• applications where just one position of S2 is required
• application where switching of S2 is not allowed.

Assembly option when resistor R17 not populated and R19 populated is equivalent to slide switch S2 permanently set to PON.

Figure 41: assembly option: S2 = PON.

Assembly option when resistor R17 populated and R19 not populated is equivalent to slide switch S2 permanently set to FX2 PON.

Figure 42: Assembly option: S2 = FX2 PON.