ATA8742-PXQW【PDF 41/238 页】MCU W/TRANSMITTER ASK/FSK 24QFN

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Sheet目录52

37页 38页 39页 40页 [41页]42页 43页 44页 45页

9151AINDCO07/09

ATA8742

14. System Clock and Clock Options

14.1 Clock Systems and their Distribution

Figure 14-1 on page 41 presents the principal clock systems in the AVR and their distribution. All

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 50. The clock systems are detailed below.

Figure 14-1. Clock Distribution

14.1.1

CPU Clock clk

CPU

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.

14.1.2

I/O Clock clk

I/O

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.

14.1.3

Flash Clock clk

FLASH

The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-

taneously with the CPU clock.

14.1.4

ADC Clock clk

ADC

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.

General I/O

Modules

CPU Core

RAM

clk

I/O

AVR Clock

Control Unit

clk

CPU

Flash and

EEPROM

clk

FLASH

Source clock

Watchdog Timer

Watchdog

Oscillator

Reset Logic

Clock

Multiplexer

Watchdog clock

Calibrated RC

Oscillator

Calibrated RC

Oscillator

External Clock

ADC

clk

ADC

Crystal

Oscillator

Low-Frequency

Crystal Oscillator

System Clock

Prescaler

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