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| 型号： | PIC16C621-20/SS |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 8-BIT, OTPROM, 20 MHz, RISC MICROCONTROLLER, PDSO20 |
| 封装： | 0.209 INCH, PLASTIC, MO-150, SSOP-20 |
| 文件页数： | 65/121页 |
| 文件大小： | 1202K |
| 代理商： | PIC16C621-20/SS |
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PIC16C62X
DS30235H-page 48
1999 Microchip Technology Inc.
9.2.3
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 9-4 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
resistor provides the
negative
feedback
for
stability.
The
10 k
potentiometers bias the 74AS04 in the linear region.
This could be used for external oscillator designs.
FIGURE 9-4:
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
Figure 9-5 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
resistors provide the negative feedback to bias
the inverters in their linear region.
FIGURE 9-5:
EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
20 pF
+5V
20 pF
10k
4.7k
10k
74AS04
XTAL
10k
74AS04
PIC16C62X
CLKIN
To Other
Devices
330 k
74AS04
PIC16C62X
CLKIN
To Other
Devices
XTAL
330 k
74AS04
0.1
F
9.2.4
RC OSCILLATOR
For timing insensitive applications the “RC” device
option offers additional cost savings. The RC oscillator
frequency is a function of the supply voltage, the
resistor (Rext) and capacitor (Cext) values, and the
operating temperature. In addition to this, the oscillator
frequency will vary from unit to unit due to normal
process
parameter
variation.
Furthermore,
the
difference in lead frame capacitance between package
types
will
also
affect
the
oscillation
frequency,
especially for low Cext values. The user also needs to
take into account variation due to tolerance of external
R and C components used. Figure 9-6 shows how the
R/C combination is connected to the PIC16C62X. For
Rext values below 2.2 k
, the oscillator operation may
become unstable or stop completely. For very high Rext
values (e.g., 1 M
), the oscillator becomes sensitive to
noise, humidity and leakage. Thus, we recommend to
keep Rext between 3 k
and 100 k.
Although the oscillator will operate with no external
capacitor (Cext = 0 pF), we recommend using values
above 20 pF for noise and stability reasons. With no or
small external capacitance, the oscillation frequency
can vary dramatically due to changes in external
capacitances, such as PCB trace capacitance or
package lead frame capacitance.
See Section 13.0 for RC frequency variation from part
to part due to normal process variation. The variation is
larger for larger R (since leakage current variation will
affect RC frequency more for large R) and for smaller C
(since variation of input capacitance will affect RC fre-
quency more).
See Section 13.0 for variation of oscillator frequency
due to VDD for given Rext/Cext values, as well as
frequency variation due to operating temperature for
given R, C and VDD values.
The oscillator frequency, divided by 4, is available on
the OSC2/CLKOUT pin, and can be used for test pur-
poses or to synchronize other logic (Figure 3-2 for
waveform).
FIGURE 9-6:
RC OSCILLATOR MODE
OSC2/CLKOUT
Cext
Rext
VDD
PIC16C62X
OSC1
FOSC/4
Internal Clock
VDD
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相关代理商/技术参数 |
参数描述 |
|---|---|
| PIC16C621A/JW | 功能描述:8位微控制器 -MCU 1.75KB 96 RAM 13 I/O RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
| PIC16C621A-04/P | 功能描述:8位微控制器 -MCU 1.75KB 96 RAM 13 I/O RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
| PIC16C621A-04/P | 制造商:Microchip Technology Inc 功能描述:IC 8BIT CMOS MCU 16C621 DIP18 |
| PIC16C621A-04/SO | 功能描述:8位微控制器 -MCU 1.75KB 96 RAM 13 I/O RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
| PIC16C621A-04/SS | 功能描述:8位微控制器 -MCU 1.75KB 96 RAM 13 I/O RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
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