Rainbow-electronics ATmega8515L Manuel d'utilisateur télécharger pdf (Page 31)

ATmega8515(L)

2512A–AVR–04/02

System Clock and

Clock Options

Clock Systems and their

Distribution

Figure17presents the principalclock systems in the AVR and theirdistribution. All of

the clocks need not beactive at a given time. Inorder to reduce powerconsumption, the

clocks to modules not being usedcan be haltedbyusing different sleep modes, as

described in “PowerManagement andSleepModes”onpage 38. The clock systems

are detailedbelow.

Figure 17. Clock Distribution

CPU Clock – clk

CPU

The CPUclock isrouted to parts of the system concernedwith operation of theAVR

core. Examples ofsuch modules arethe General PurposeRegisterFile, the Status Reg-

ister, and the data memory holding the Stack Pointer. Halting the CPUclock inhibits the

core from performing general operations andcalculations.

I/O Clock – clk

I/O

The I/Oclock is usedbythemajority of the I/O modules, likeTimer/Counters, SPI, and

USART. The I/Oclock is alsousedbythe ExternalInterruptmodule,but note that some

external interrupts are detectedbyasynchronouslogic, allowing such interrupts to be

detected even if the I/Oclock ishalted.

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

Crystal

Oscillator

Low-frequency

Crystal Oscillator

External RC

Oscillator

External Clock

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 222 223

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Rainbow-electronics ATmega8515L Manuel d'utilisateur Page 31

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