atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 26

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

6. System Clock and Clock Options
6.1
6.1.1
6.1.2
6.1.3
26
Clock Systems and their Distribution
ATmega32U4
CPU Clock – clk
I/O Clock – clk
Flash Clock – clk
I/O
Figure 6-1
need not be active at a given time. In order to reduce power consumption, the clocks to modules
not being used can be halted by using different sleep modes, as described in
ment and Sleep Modes” on page
Figure 6-1.
The CPU clock is routed to parts of the system concerned with operation of the AVR core.
Examples of such modules are the General Purpose Register File, the Status Register and the
data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing
general operations and calculations.
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART.
The I/O clock is also used by the External Interrupt module, but note that some external inter-
rupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O
clock is halted. Also, TWI address recognition is handled in all sleep modes.
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
CPU
FLASH
USB
(1)
presents the principal clock systems in the AVR and their distribution. All of the clocks
PLL Postcaler
Multiplexer
PLL Input
PLL
Clock Distribution
clk
PLL
High Speed
(2)
Timer
PLL Clock
Prescaler
clk
I/O
41. The clock systems are detailed below.
General I/O
Modules
Oscillator
Crystal
clk
PllPresc
System Clock
Clock Switch
Control Unit
AVR Clock
Multiplexer
Prescaler
Clock
External Clock
Source clock
ADC
clk
ADC
clk
clk
Reset Logic
CPU Core
CPU
FLASH
Watchdog
Oscillator
Watchdog Timer
Watchdog
clock
RAM
“Power Manage-
Calibrated RC
Oscillator
Flash and
EEPROM
7766A–AVR–03/08