AT89C51ID2-RDTIM datasheet(15/159 Pages) ATMEL

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AT89C51ID2

4289A–8051–09/03

Oscillators

Overview

Two oscillators are available for CPU:

•

OSCA used for high frequency: Up to 40 MHz

•

OSCB used for low frequency: 32.768 kHz

Several operating modes are available and programmable by software:

•

to switch OSCA to OSCB and vice-versa

•

to stop OSCA or OSCB to reduce consumption

In order to optimize the power consumption and the execution time needed for a specific

task, an internal prescaler feature has been implemented between the selected oscilla-

tor and the CPU.

Registers

Table 15. CKSEL Register

CKSEL - Clock Selection Register (85h)

Reset Value = 0000 000’HSB.OSC’b (see Hardware Security Byte (HSB))

Not bit addressable

7654

3210

-------

CKS

Bit

Number

Bit

Mnemonic

Description

Reserved

0CKS

CPU Oscillator Select Bit: (CKS)

Cleared, CPU and peripherals connected to OSCB

Set, CPU and peripherals connected to OSCA

Programmed by hardware after a Power-up regarding Hardware Security Byte

(HSB).HSB.OSC (Default setting, OSCA selected)

AT89C51ID2-RDTIM 数据表(PDF) 15 Page - ATMEL Corporation

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