ATmega32U2 datasheet(193/314 Pages) ATMEL

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7799B–AVR–07/09

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.

Idle mode

Active mode

USBE=1

& DETACH=0

& suspend

USBE=0

| DETACH=1

| suspend

ATmega32U2 Datasheet(PDF) 193 Page - ATMEL Corporation