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PDF AN663 Data sheet ( Hoja de datos )
| Número de pieza | AN663 | |
| Descripción | MCU | |
| Fabricantes | Silicon Laboratories | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AN663 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
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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.
Oscillator Name
Table 1. AHB Clock Source Summary
Short Name
Module
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Frequency
Use Case
Low Power
Oscillator
LPOSCn
LPOSCn
20 MHz or 2.5 MHz
High frequency and lower
power consumption required
Low Frequency
Oscillator
LFOSCn
RTCn
16.4 kHz
Low power, slow frequency
required; no room for exter-
nal RTC watch crystal
RTC Oscillator
RTCnOSC
RTCn
32.768 kHz
Low power, slow, accurate
frequency required; room for
external RTC watch crystal
External Oscillator EXTOSCn
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
PLLnOSC
PLLn
23 MHz to maximum device Flexible, fast, and accurate
frequency
frequency required
USB Oscillator USBnOSC
USBn
48 MHz
Very accurate fast fre-
quency required; no flexibil-
ity needed
Rev. 0.1 2/12
Copyright © 2012 by Silicon Laboratories
AN663
Datasheet pdf - http://www.DataSheet4U.co.kr/
1 page  
AN663
2.4. External Oscillator (EXTOSCn)
The AHB clock may be derived from the external oscillator module. The external oscillator supports four different
external oscillators: crystal, CMOS, RC, and C.
Figure 4 depicts a block diagram for the external oscillator module.
External RC
Oscillator
VIO
External C
Oscillator
XTAL2
XTAL2
EXTOSCn Module
External Crystal
XTAL1
10 M
XTAL2
External CMOS
Oscillator
XTAL2
XTAL1
XTAL2
External Oscillator
Control
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EXTOSCn Clock
Figure 4. External Oscillator Block Diagram
Rev. 0.1
5
Datasheet pdf - http://www.DataSheet4U.co.kr/
5 Page 
AN663
3. Clocks and the Peripherals
The APB clock drives most peripherals and their registers. The exceptions to this are lower power peripherals that
run from the RTC Oscillator or the Low Frequency Oscillator directly.
For peripherals that run from the APB clock, disabling the clock to the module in the device clock control module
(CLKCTRL) will disable the clock to both the module and the module’s registers. For peripherals that run from
another clock source, disabling the clock to the module will disable the clock to the module’s registers only and the
module will continue to run.
4. Reset Behavior
On SiM3xxxx devices, the low power oscillator (LPOSCn) is the default oscillator after a reset. In addition, the
clocks to most peripherals are disabled 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.
www.DataSheet.net/
Rev. 0.1
11
Datasheet pdf - http://www.DataSheet4U.co.kr/
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet AN663.PDF ] | |
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