atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 286

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

23.4
23.5
23.6
286
USB reset
Endpoint selection
Endpoint activation
ATmega32U4
The data toggle field remains unchanged.
The other registers remain unchanged.
The endpoint configuration remains active and the endpoint is still enabled.
The endpoint reset may be associated with a clear of the data toggle command (RSTDT bit) as
an answer to the CLEAR_FEATURE USB command.
When an USB reset is detected on the USB line (SE0 state with a minimum duration of 2.5µs),
the next operations are performed by the controller:
If the CPU hardware reset function is activated (RSTCPU bit set in UDCON register), a reset is
generated to the CPU core without disabling the USB controller (that follows the same behavior
than after a standard USB End of Reset, and remains attached). That feature may be used to
enhance device reliability.
Prior to any operation performed by the CPU, the endpoint must first be selected. This is done
by setting the EPNUM2:0 bits (UENUM register) with the endpoint number which will be man-
aged by the CPU.
The CPU can then access to the various endpoint registers and data.
The endpoint is maintained under reset as long as the EPEN bit is not set.
The following flow must be respected in order to activate an endpoint:
• the UEINTX, UESTA0X and UESTA1X are restored to their reset value.
• all the endpoints are disabled
• the default control endpoint remains configured (see Section 23.3, page 285 for more
details).
7766A–AVR–03/08