ATAR080 datasheet(15/68 Pages) ATMEL

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ATAR080

4675D–4BMCU–12/04

Oscillator Circuits and

External Clock Input Stage

The ATAR080 consists of four different internal oscillators: two RC-oscillators, one

4-MHz crystal oscillator, one 32-kHz crystal oscillator and one external clock input

stage.

RC-oscillator 1 Fully Integrated

For timing insensitive applications, it is possible to use the fully integrated

RC-oscillator 1. It operates without any external components and saves additional

costs. The RC-oscillator 1 center frequency tolerance is better than ±50% over the full

temperature and voltage range. The basic center frequency of the RC-oscillator 1 is

0 ≈

3.8 MHz. The RC-oscillator 1 is selected by default after power-on reset.

Figure 15. RC-oscillator 1

External Input Clock

The OSC1 or OSC2 (mask option) can be driven by an external clock source provided it

meets the specified duty cycle, rise and fall times and input levels. Additionally, the

external clock stage contains a supervisory circuit for the input clock. The supervisor

function is controlled via the OS1, OS0-bit in the SC register and the CCS-bit in the

CM-register. If the external input clock fails and CCS = 0 is set in the CM-register, the

supervisory circuit generates a hardware reset. The input clock has failed if the fre-

quency is less than 500 kHz for more than 1 ms.

Figure 16. External Input Clock

Table 5. Supervisor Function Control Bits

RC-oscillator 1

RcOut1

Stop

Control

RcOut1

Osc-Stop

OS1

OS0

CCS

Supervisor Reset Output (Res)

Enable

Disable

Ext. input clock

ExOut

Stop

Ext.

Clock

RcOut1

Osc-Stop

ExIn

CCS

Res

OSC1

OSC2

Clock monitor

ATAR080 Datasheet(PDF) 15 Page - ATMEL Corporation

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