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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 (FX2 PON), the 1.2 V and 2.5 V power rails 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 switches the 1.2 V and 2.5 V power rails on, if enough current is available from the USB bus.
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S2 position | Default position | Effect on 1.2 V and 2.5 V rails |
|---|---|---|
FX2 PON (on) |  | 1.2 V and 2.5 V rails controlled by USB FX2 microcontroller (signal FX2_PS_EN) PS_EN = FX2_PS_EN = high or low |
PON (off) |  | 1.2 V and 2.5 V rails always enabled (PS_EN = high) PS_EN ≠ FX_PS_EN |
Table 14: Slide switch S2 settings overview (1.2 V and 2.5 V rails 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 (high) or disables (low) power rails 2.5V and 1.2V.
Figure 36: Power rails 2.5V and 1.2V could be enabled/disabled by signal PS_EN. Power-rail 3.3V is not controlled by signal PS_EN and is unconditionally enabled.
Figure 38: Power rails 3.3V could not be enabled/disabled by signal PS_EN.
VCCIO assembly options
According to the corresponding assembly option, power rail VCCCIO0 can depend or not on the 2.5V power rail.
Figure 37: example of VCCIO0 assembly not dependent on 2.5V power rail. The other way is also possible.
Slide Switch S2 = FX2 PON
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Figure 35: S2 on position FX2 PON (PS_EN = FX2_PS_EN = high or low ).
Figure 36: Slide switch S2 schematic.
Figure 37: 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.
- Dynamic full power operation (PS_EN = high): when the EZ-USB FX2LP USB FX2 microcontroller sets signal PS_EN = FX2_PS_EN = high, power rails 2.5V and 1.2V are enabled.
This setting can be useful for . - Dynamic low power operation (PS_EN = low): 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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Slide Switch S2 = PON
Full power operation ( (PS_EN = high): 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 2.5V and 1.2V are unconditionally enabled.
Figure 34: S2 on position PON (PS_EN ≠ FX2_PS_EN = x; PS_EN = high ).
Signal PS_EN
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Power-rail 3.3V is not controlled by signal PS_EN and is unconditionally enabled.
Figure 38: Power rails 3.3V could not be enabled/disabled by signal PS_EN.
VCCIO assembly options
According to the corresponding assembly option, power rail VCCCIO0 can depend or not on the 2.5V power rail.
Figure 37: example of VCCIO0 assembly not dependent on 2.5V power rail. The other way is also possible.
Summary table
Table 14 summarizes all switching options implied by slide switch S2 and firmware signal FX2_PS_EN (under the standard assembly option).
power rail | S2= PON | S2 = FX2 PON and | S2 = FX2 PON and |
|---|---|---|---|
1.2V | on | on | off |
2.5V | on | on | off |
VCCCIO0 (= 2.5V) | on | on | off |
VCCCIO0 (= 3.3V) | on | on | on |
(2) R131 soldered / R132 unsoldered
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