AT90CAN128-UL View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT90CAN128-UL

8-bit Microcontroller with 128K Bytes of ISP Flash and CAN Controller

Atmel Corporation 

System Clock

Clock Systems and

their Distribution

Figure 19 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 unused modules can be halted by using different sleep modes, as described in

“Power Management and Sleep Modes” on page 43. The clock systems are detailed

below.

Figure 19. Clock Distribution

Asynchronous

Timer/Counter2

CAN

Controller

General I/O

Modules

ADC

CPU Core

RAM

Flash and

EEPROM

CLKO

CKOUT Fuse

Multiplexer

clkI/O

clkASY

clkADC

AVR Clock

Control Unit

clkCPU

clkFLASH

Reset Logic

Watchdog Timer

Prescaler

Source clock

Clock

Multiplexer

Watchdog clock

Watchdog

Oscillator

Timer/Counter2

External Clock

Timer/Counter2

Oscillator

External Clock

Crystal

Oscillator

Low-frequency

Crystal Oscillator

Calibrated RC

Oscillator

TOSC1

TOSC2

XTAL1

XTAL2

CPU Clock – clkCPU

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 Reg-

ister and the data memory holding the Stack Pointer. Halting the CPU clock inhibits the

core from performing general operations and calculations.

I/O Clock – clkI/O

The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, CAN,

USART. 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. Also note that address recognition in the TWI

module is carried out asynchronously when clkI/O is halted, enabling TWI address recep-

tion in all sleep modes.

Flash Clock – clkFLASH

The Flash clock controls operation of the Flash interface. The Flash clock is usually

active simultaneously with the CPU clock.

Asynchronous Timer Clock – The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked

clkASY

directly from an external clock or an external 32 kHz clock crystal. The dedicated clock

34 AT90CAN128

4250E–CAN–12/04

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