PIC16F627A-I/P【PDF 3/180 页】IC MCU FLASH 1KX14 EEPROM 18DIP

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录3880

1页 2页 [3页]4页 5页 6页 7页

PIC16F627A/628A/648A

DS40044G-page 100

2009 Microchip Technology Inc.

14.2.3

EXTERNAL CRYSTAL OSCILLATOR

CIRCUIT

Either a prepackaged oscillator can be used or a simple

oscillator circuit with TTL gates can be built.

Prepackaged oscillators provide a wide operating

range and better stability. A well-designed crystal

oscillator will provide good performance with TTL

gates. Two types of crystal oscillator circuits can be

used; one with series resonance, or one with parallel

resonance.

Figure 14-2 shows implementation of a parallel

resonant oscillator circuit. The circuit is designed to

use the fundamental frequency of the crystal. The

74AS04 inverter performs the 180

° phase shift that a

parallel oscillator requires. The 4.7 k

Ω resistor

provides the negative feedback for stability. The

10 k

Ω potentiometers bias the 74AS04 in the linear

region. This could be used for external oscillator

designs.

FIGURE 14-2:

EXTERNAL PARALLEL

RESONANT CRYSTAL

OSCILLATOR CIRCUIT

Figure 14-3 shows a series resonant oscillator circuit.

This circuit is also designed to use the fundamental

frequency of the crystal. The inverter performs a 180

phase shift in a series resonant oscillator circuit. The

330 k

Ω resistors provide the negative feedback to bias

the inverters in their linear region.

FIGURE 14-3:

EXTERNAL SERIES

RESONANT CRYSTAL

OSCILLATOR CIRCUIT

14.2.4

PRECISION INTERNAL 4 MHZ

OSCILLATOR

The internal precision oscillator provides a fixed 4 MHz

(nominal) system clock at VDD = 5V and 25

°C. See

Section 17.0 “Electrical Specifications”

, for informa-

tion on variation over voltage and temperature.

14.2.5

EXTERNAL CLOCK IN

For applications where a clock is already available

elsewhere, users may directly drive the PIC16F627A/

628A/648A provided that this external clock source meets

the AC/DC timing requirements listed in Section 17.6

“Timing Diagrams and Specifications”

. Figure 14-4

below shows how an external clock circuit should be

configured.

FIGURE 14-4:

EXTERNAL CLOCK INPUT

OPERATION (EC, HS, XT

OR LP OSC

CONFIGURATION)

+5V

10K

4.7K

10K

74AS04

XTAL

10K

74AS04

PIC16F627A/628A/648A

CLKIN

To other

Devices

330 K

74AS04

PIC16F627A/

CLKIN

To other

Devices

XTAL

330 K

74AS04

0.1 pF

628A/648A

Clock from

ext. system

PIC16F627A/628A/648A

RA6

RA7/OSC1/CLKIN

RA6/OSC2/CLKOUT

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式