ATMEGA8U2_14 Datasheet, PDF (193/310 Pages) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

ATmega8U2/16U2/32U2
• Endpoints activation:
Endpoint 0 to Endpoint 4 are configured, in the growing order. The memory of each is
reserved in the DPRAM.
• Endpoint disable:
The Endpoint 2 is disabled (EPEN=0), but its memory reservation is internally kept by the
controller.
• Free its memory:
The ALLOC bit is cleared: the Endpoint 3 slides down, but the Endpoint 4 does not slide.
• Endpoint activation:
The firmware chooses to reconfigure the Endpoint 2, but with a bigger size. The controller
reserved the memory after the endpoint 1 memory and automatically slide the Endpoint 3.
The Endpoint 4 does not move and a memory conflict appear, in that both Endpoint 3 and 4
use a common area. The data of those endpoints are potentially lost.
Note that:
• The data of Endpoint 0 is never lost at activation or deactivation of a higher Endpoint. The
data is lost only if the Endpoint 0 is deactivated.
• Deactivate and reactivate the same Endpoint with the same parameters does not lead to a
slide of the higher endpoints. For those endpoints, the data are preserved.
• CFGOK is set by hardware even in the case that there is a “conflict” in the memory allocation.
20.7
PAD suspend
The next figures illustrates the pad behaviour:
• In the Idle mode, the pad is put in low power consumption mode.
• In the Active mode, the pad is working.
Figure 20-11. Pad behaviour
The SUSPI flag indicated that a suspend state has been detected on the USB bus. This flag
automatically put the USB pad in Idle. The detection of a non-idle event sets the WAKEUPI flag
and wakes-up the USB pad.
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