
EZ-USB FX2 Technical Reference Manual
Page 6-4 EZ-USB FX2 Technical Reference Manual v2.1
FX2 firmware responds to the SUSPEND interrupt by taking the following actions:
1. Perform any necessary housekeeping such as shutting off external power-consuming devices.
2. Set bit 0 of the PCON register.
These actions put the FX2 into a low power ‘suspend’ state, as required by the USB Specification.
6.2.1 SUSPEND Register
FX2 firmware can force the chip into its low-power mode at any time, even without detecting a
3-millisecond “J” state on the USB bus. This “unconditional suspend” functionality is useful in
applications which require the FX2 to enter its low-power mode even while disconnected from the
USB bus.
To force the FX2 unconditionally to enter its low-power mode, firmware simply writes any value to
the SUSPEND register (at 0xE681) before setting the PCON.0 bit.
6.3 Wakeup/Resume
Figure 6-3. FX2 Wakeup/Resume sequence
PLL
Oscillator
divider
8051
CLKOUT
24 MHz
START
USB RESUME
WAKEUP pin
"WAKEUP" INT
Signal
Resume
(USBCS.0)
Restart
Delay
WU2 pin
DPEN
WUEN
WU2EN
WUPOL
WU2POL
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