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PIC16F688-I/ST 参数 Datasheet PDF下载

PIC16F688-I/ST图片预览
型号: PIC16F688-I/ST
PDF下载: 下载PDF文件 查看货源
内容描述: 14引脚基于闪存的8位CMOS微控制器采用纳瓦技术 [14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology]
分类和应用: 闪存微控制器
文件页数/大小: 202 页 / 3832 K
品牌: MICROCHIP [ MICROCHIP ]
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PIC16F688  
3.4.4  
EXTERNAL RC MODES  
3.5  
Internal Clock Modes  
The external Resistor-Capacitor (RC) modes support  
the use of an external RC circuit. This allows the  
designer maximum flexibility in frequency choice while  
keeping costs to a minimum when clock accuracy is not  
required. There are two modes: RC and RCIO.  
The Oscillator module has two independent, internal  
oscillators that can be configured or selected as the  
system clock source.  
1. The HFINTOSC (High-Frequency Internal  
Oscillator) is factory calibrated and operates at  
8 MHz. The frequency of the HFINTOSC can be  
user-adjusted via software using the OSCTUNE  
register (Register 3-2).  
In RC mode, the RC circuit connects to OSC1. OSC2/  
CLKOUT outputs the RC oscillator frequency divided  
by 4. This signal may be used to provide a clock for  
external circuitry, synchronization, calibration, test or  
other application requirements. Figure 3-5 shows the  
external RC mode connections.  
2. The LFINTOSC (Low-Frequency Internal  
Oscillator) is uncalibrated and operates at 31 kHz.  
The system clock speed can be selected via software  
using the Internal Oscillator Frequency Select bits  
IRCF<2:0> of the OSCCON register.  
FIGURE 3-5:  
EXTERNAL RC MODES  
The system clock can be selected between external or  
internal clock sources via the System Clock Selection  
(SCS) bit of the OSCCON register. See Section 3.6  
“Clock Switching” for more information.  
VDD  
PIC® MCU  
REXT  
OSC1/CLKIN  
Internal  
Clock  
3.5.1 INTOSC AND INTOSCIO MODES  
CEXT  
VSS  
The INTOSC and INTOSCIO modes configure the  
internal oscillators as the system clock source when  
the device is programmed using the oscillator selection  
or the FOSC<2:0> bits in the Configuration Word  
register (CONFIG). See Section 11.0 “Special  
Features of the CPU” for more information.  
(1)  
FOSC/4 or  
OSC2/CLKOUT  
(2)  
I/O  
Recommended values: 10 kΩ ≤ REXT 100 kΩ, <3V  
3 kΩ ≤ REXT 100 kΩ, 3-5V  
In INTOSC mode, OSC1/CLKIN is available for general  
purpose I/O. OSC2/CLKOUT outputs the selected  
internal oscillator frequency divided by 4. The CLKOUT  
signal may be used to provide a clock for external  
circuitry, synchronization, calibration, test or other  
application requirements.  
CEXT > 20 pF, 2-5V  
Note 1: Alternate pin functions are listed in  
Section 1.0 “Device Overview”.  
2: Output depends upon RC or RCIO clock mode.  
In RCIO mode, the RC circuit is connected to OSC1.  
OSC2 becomes an additional general purpose I/O pin.  
In INTOSCIO mode, OSC1/CLKIN and OSC2/CLKOUT  
are available for general purpose I/O.  
The RC oscillator frequency is a function of the supply  
voltage, the resistor (REXT) and capacitor (CEXT) values  
and the operating temperature. Other factors affecting  
the oscillator frequency are:  
3.5.2  
HFINTOSC  
The High-Frequency Internal Oscillator (HFINTOSC) is  
a factory calibrated 8 MHz internal clock source. The  
frequency of the HFINTOSC can be altered via  
software using the OSCTUNE register (Register 3-2).  
• threshold voltage variation  
• component tolerances  
• packaging variations in capacitance  
The output of the HFINTOSC connects to a postscaler  
and multiplexer (see Figure 3-1). One of seven  
frequencies can be selected via software using the  
IRCF<2:0> bits of the OSCCON register. See  
Section 3.5.4 “Frequency Select Bits (IRCF)” for  
more information.  
The user also needs to take into account variation due  
to tolerance of external RC components used.  
The HFINTOSC is enabled by selecting any frequency  
between 8 MHz and 125 kHz by setting the IRCF<2:0>  
bits of the OSCCON register 000. Then, set the  
System Clock Source (SCS) bit of the OSCCON  
register to ‘1’ or enable Two-Speed Start-up by setting  
the IESO bit in the Configuration Word register  
(CONFIG) to ‘1’.  
The HF Internal Oscillator (HTS) bit of the OSCCON  
register indicates whether the HFINTOSC is stable or not.  
© 2007 Microchip Technology Inc.  
DS41203D-page 25  
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