Datasheet > AN663

AN663

更新时间： 2022-05-16 20:15:30

品牌	Logo	应用领域
芯科 - SILICON		时钟
页数	文件大小	规格书
12页	84K
描述
PRECISION32â¢ MCU FAMILY CLOCKING OPTIONS

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AN663 数据手册

AN663

PRECISION32™ MCU FAMILY CLOCKING OPTIONS

1. Introduction

The 32-bit Precision32™ MCU family features a highly configurable clock structure. The advanced high-

performance bus (AHB) and advanced peripheral bus (APB) have many options available for clocking. In addition,

firmware can disable most peripheral clocks to save power.

The clock to the module must be enabled before firmware can modify the registers. The first initialization

step in all peripheral initialization routines should enable the clock to the module.

The corresponding Precision32 family reference manual contains detailed descriptive and usage information on

each of the clock sources mentioned in this document.

2. Clock Sources

The AHB drives the core and memory on ARM Cortex™-M3 devices. The APB drives the peripherals and

peripheral registers.

The AHB on the Precision32 devices has several options for clock sources: Low Power Oscillator, Low Frequency

Oscillator, RTC Oscillator, External Oscillator, PLL Oscillator, and USB Oscillator. The APB clock is either equal to

AHB or a divide by 2 version of it, so it is always synchronized with the AHB clock.

Table 1 describes the oscillators that can serve as clock sources for the AHB bus. Figure 1 shows an example

clock control block diagram.

Table 1. AHB Clock Source Summary

Oscillator Name

Short Name

Module

Frequency

Use Case

Low Power

Oscillator

LPOSCn

20 MHz or 2.5 MHz

High frequency and lower

power consumption required

Low Frequency

Oscillator

LFOSCn

RTCnOSC

EXTOSCn

RTCn

16.4 kHz

Low power, slow frequency

required; no room for exter-

nal RTC watch crystal

RTC Oscillator

32.768 kHz

Low power, slow, accurate

frequency required; room for

external RTC watch crystal

External Oscillator

EXTOSCn

Crystal: 10 kHz to 25 MHz

CMOS: 10 kHz to 50 MHz

RC or C: up to 1.6 MHz

Very accurate frequency

required; room for external

components

PLL Oscillator

USB Oscillator

PLLnOSC

USBnOSC

PLLn

23 MHz to maximum device Flexible, fast, and accurate

frequency

frequency required

USBn

48 MHz

Very accurate fast fre-

quency required; no flexibil-

ity needed

Rev. 0.1 2/12

AN663

12 3 4 5 6 7...12

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