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參數(shù)資料
| 型號： | PIC16C925/L |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | 8-BIT, OTPROM, 20 MHz, RISC MICROCONTROLLER, PQCC68 |
| 封裝： | PLASTIC, LCC-68 |
| 文件頁數(shù)： | 5/183頁 |
| 文件大?。?/td> | 3233K |
| 代理商： | PIC16C925/L |
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PIC16C925/926
DS39544A-page 100
Preliminary
2001 Microchip Technology Inc.
12.2.3
EXTERNAL CRYSTAL OSCILLATOR
CIRCUIT
Either a prepackaged oscillator can be used, or a sim-
ple oscillator circuit with TTL gates can be built. Pre-
packaged 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 12-3 shows implementation of a parallel reso-
nant oscillator circuit. The circuit is designed to use the
fundamental frequency of the crystal. The 74AS04
inverter performs the 180-degree phase shift that a par-
allel oscillator requires. The 4.7 k
resistor provides
the negative feedback for stability. The 10 k
potenti-
ometer biases the 74AS04 in the linear region. This
could be used for external oscillator designs.
FIGURE 12-3:
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
Figure 12-4 shows a series resonant oscillator circuit.
This circuit is also designed to use the fundamental fre-
quency of the crystal. The inverter performs a
180-degree phase shift in a series resonant oscillator
circuit. The 330 k
resistors provide the negative feed-
back to bias the inverters in their linear region.
FIGURE 12-4:
EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
12.2.4
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 resis-
tor (REXT) and capacitor (CEXT) values, and the operat-
ing temperature. In addition to this, the oscillator
frequency will vary from unit to unit due to normal pro-
cess 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 compo-
nents used. Figure 12-5 shows how the R/C combina-
tion is connected to the PIC16CXXX. 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 pack-
age lead frame capacitance.
See characterization data for desired device for RC fre-
quency variation from part to part, due to normal pro-
cess 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 frequency more).
See characterization data for desired device for varia-
tion 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 (see Figure 1-2 for
waveform).
FIGURE 12-5:
RC OSCILLATOR MODE
20 pF
+5V
20 pF
10k
4.7k
10k
74AS04
XTAL
10k
74AS04
CLKIN
To Other
Devices
PIC16CXXX
330 k
74AS04
PIC16CXXX
CLKIN
To Other
Devices
XTAL
330 k
74AS04
0.1
F
OSC2/CLKOUT
CEXT
VDD
REXT
VSS
PIC16CXXX
OSC1
FOSC/4
Internal
Clock
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| PIC16C925T-I/L | 功能描述:8位微控制器 -MCU 7KB 176 RAM 52 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
| PIC16C925T-I/PT | 功能描述:8位微控制器 -MCU 7KB 176 RAM 52 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
| PIC16C926/CL | 功能描述:8位微控制器 -MCU 14KB 336 RAM 52 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
| PIC16C926-I/L | 功能描述:8位微控制器 -MCU 14KB 336 RAM 52 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
| PIC16C926-I/L | 制造商:Microchip Technology Inc 功能描述:8BIT CMOS MCU SMD 16C926 PLCC68 |
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