atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 276

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

22.4
22.4.1
22.4.2
22.4.3
276
General Operating Modes
ATmega32U4
Introduction
Power-on and reset
Interrupts
The USB controller is disabled and reset after an hardware reset generated by:
But another available and optional CPU reset source is:
In this case, the USB controller is reset, but not disabled (so that the device remains attached).
The next diagram explains the USB controller main states on power-on:
Figure 22-7. USB controller states after reset
USB Controller state after an hardware reset is ‘Reset’. In this state:
After setting USBE, the USB Controller enters the Device state. The controller is ‘Idle’.
The USB Controller can at any time be stopped by clearing USBE. In fact, clearing USBE acts
as an hardware reset.
Two interrupts vectors are assigned to USB interface.
• USBE is not set
• the USB controller clock is stopped in order to minimize the power consumption
• the USB controller is disabled,
• the USB pad is in the suspend mode,
• the Device USB controller internal state is reset.
(FRZCLK=1),
– Power on reset
– External reset
– Watchdog reset
– Brown out reset
– JTAG reset
– USB End Of Reset
Clock stopped
Device
FRZCLK=1
Macro off
USBE=1
USBE=0
Reset
USBE=0
RESET
HW
USBE=0
<any other
state>
7766A–AVR–03/08