ATMEGA8U2_14 Datasheet, PDF (200/310 Pages) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

ATmega8U2/16U2/32U2
UADD contains the default address 00h after a power-up or an USB reset.
ADDEN is cleared by hardware:
• after a power-up reset,
• when an USB reset is received,
• or when the macro is disabled (USBE cleared)
When this bit is cleared, the default device address 00h is used.
21.8
Suspend, Wake-up and Resume
After the USB line has been inactive for a period of 3 ms (J state), the controller set the SUSPI
flag and triggers the corresponding interrupt if enabled. The firmware may then set the FRZCLK
bit.
The CPU can also, depending on software architecture, disable the PLL and/or enter in the idle
mode to reduce the power consumption (especially in a bus powered application).
There are two ways to recover from the Suspend mode:
1. Clear the FRZCLK bit. This is possible if the CPU is not in the Idle mode.
2. If the CPU is in idle mode, enable the WAKEUPI interrupt (WAKEUPE set). Then, as
soon as an non-idle signal is seen by the controller, the WAKEUPI interrupt is triggered.
The firmware shall then clear the FRZCLK bit to restart the transfer.
There are no relationship between the SUSPI interrupt and the WAKEUPI interrupt: the WAKE-
UPI interrupt is triggered as soon as there are non-idle patterns on the data lines. Thus, the
WAKEUPI interrupt can occurs even if the controller is not in the “suspend” mode.
When the WAKEUPI interrupt is triggered, if the SUSPI interrupt bit was already set, it is cleared
by hardware.
When the SUSPI interrupt is triggered, if the WAKEUPI interrupt bit was already set, it is cleared
by hardware.
21.9 Detach
The reset value of the DETACH bit is 1.
It is possible to re-enumerate a device, simply by setting and clearing the DETACH bit (the line
discharge time must be taken in account).
• When the USB device controller is in full-speed mode, setting DETACH will disconnect the
pull-up on the D+. Then, clearing DETACH will connect the pull-up on the D+.
Figure 21-3. Detach a device in Full-speed:
7799D–AVR–11/10
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