ATA8741 ATMEL Corporation, ATA8741 Datasheet - Page 41

• Manufacturer Part Number: ATA8741
• Manufacturer: ATMEL Corporation

14. System Clock and Clock Options
14.1
14.1.1
14.1.2
14.1.3
14.1.4
9140B–INDCO–07/09
Clock Systems and their Distribution
CPU Clock – clk
I/O Clock – clk
Flash Clock – clk
ADC Clock – clk
I/O
Figure 14-1 on page 41
of the clocks 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
“Power Management and Sleep Modes” on page
Figure 14-1. Clock Distribution
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/Counter. The I/O clock is
also used by the External Interrupt module, but note that some external interrupts are detected
by asynchronous logic, allowing such interrupts to be detected even if the I/O clock is halted.
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks
in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion
results.
CPU
ADC
FLASH
ADC
External Clock
clk
clk
ADC
I/O
Source clock
presents the principal clock systems in the AVR and their distribution. All
General I/O
System Clock
Modules
Control Unit
AVR Clock
Multiplexer
Prescaler
Clock
Calibrated RC
Oscillator
Oscillator
Crystal
Reset Logic
CPU Core
clk
clk
CPU
FLASH
Crystal Oscillator
Low-Frequency
50. The clock systems are detailed below.
Watchdog Timer
Watchdog clock
RAM
Watchdog
Oscillator
Flash and
EEPROM
Calibrated RC
Oscillator
ATA8741
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