ATAM894 datasheet(16/97 Pages) ATMEL

16 / 97 page

4679D–4BMCU–05/05

ATAM894

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 the 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-oscillator, 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 monitors

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 5-12.

Clock Module

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-oscillator 2

RCOut2

Stop

Trim

4-MHz oscillator

4Out

Stop

Oscin

Oscout

Oscin

Oscout

32-kHz oscillator

32Out

Oscin

Oscout

RC-

oscillator 1

RCOut1

Control

Stop

IN1

IN2

Cin

Divider

Sleep

WDL

Osc-Stop

NSTOP

CCS

CSS1

CSS0

CM:

BOT

- - -

OS1

OS0

SUBCL

SYSCL

SC:

OSC1

OSC2

configurable

Cin/16

32 kHz

Table 5-4.

Clock Modes

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

Cin/16

RC-oscillator 1 (intern)

32-kHz oscillator

32 kHz

ATAM894 Datasheet(PDF) 16 Page - ATMEL Corporation

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