
Chapter 6. Power Management Page 6-3
6.2 USB Suspend
Figure 6-2. USB Suspend sequence
A USB device recognizes a SUSPEND request as three milliseconds of the bus-idle (“J”) state.
When the FX2 detects this condition, it asserts the USB interrupt (INT2) and the SUSPEND inter-
rupt autovector (vector #3).
If the CPU is in reset when a SUSPEND condition is detected on the bus, the FX2 will automati-
cally turn off its oscillators (and keep the CPU in reset) until an enabled wakeup source is
asserted.
The bus-idle (“J”) state is
not
equivalent to the disconnected-from-USB state; the “J” state means
that the voltage on D+ is higher than that on D-.
PLL
Oscillator
divider
8051
CLKOUT
24 MHz
PCON.0
STOP
USB
"SUSPEND"
Interrupt
No USB activity
for 3 msec.
Signal
Resume
(USBCS.0)
Write any value to
SUSPEND register
(0xE681)
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