ATAR080 datasheet(14/68 Pages) ATMEL

14 / 68 page

ATAR080

4675D–4BMCU–12/04

The clock module is programmable via software with the clock management register

(CM) and the system configuration register (SC). The required oscillator configuration

can be selected with the OS1-bit and the OS0-bit in the SC register. A programmable

4-bit divider stage allows the adjustment of the system clock speed. A special feature of

clock management is that an external oscillator may be used and switched on and off

via a port pin for the power-down mode. Before the external clock is switched off, the

internal RC-oscillator 1 must be selected with the CCS-bit and then the SLEEP mode

may be activated. In this state an interrupt can wake up the controller with the RC-oscil-

lator, and the external oscillator can be activated and selected by software. A

synchronization stage avoids clock periods that are too short if the clock source or the

clock speed is changed. If an external input clock is selected, a supervisor circuit moni-

tors the external input and generates a hardware reset if the external clock source fails

or drops below 500 kHz for more than 1 ms.

Figure 14. Clock Module

Table 4. Clock Modes

The clock module generates two output clocks. One is the system clock (SYSCL) and

the other the periphery (SUBCL). The SYSCL can supply the core and the peripherals

and the SUBCL can supply only the peripherals with clocks. The modes for clock

sources are programmable with the OS1-bit and OS0-bit in the SC register and the

CCS-bit in the CM-register.

Ext. clock

ExIn

ExOut

Stop

RC oscillator2

RCOut2

Stop

Trim

4-MHz oscillator

4Out

Stop

Oscin

Oscout

Oscin

Oscout

32-kHz oscillator

32Out

Oscin

Oscout

oscillator 1

RCOut1

Control

Stop

IN1

IN2

Cin

Divider

Sleep

WDL

Osc-Stop

NSTOP

CCS

CSS1

CSS0

BOT

- - -

OS1

OS0

SUBCL

SYSCL

OSC1

OSC2

Cin/16

32 kHz

Mode

OS1

OS0

Clock Source for SYSCL

Clock Source for

SUBCL

CCS = 1

CCS = 0

RC-oscillator 1 (intern) External input clock

in/16

RC-oscillator 1 (intern)

RC-oscillator 2 with

external trimming

resistor

in/16

RC-oscillator 1 (intern) 4-MHz oscillator

in/16

RC-oscillator 1 (intern) 32-kHz oscillator

32 kHz

ATAR080 Datasheet(PDF) 14 Page - ATMEL Corporation

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