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| 型号： | MC68332AMEH16 |
| 厂商： | FREESCALE SEMICONDUCTOR INC |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 32-BIT, 16 MHz, MICROCONTROLLER, PQFP132 |
| 封装： | 0.950 X 0.950 INCH, 0.025 INCH PITCH, PLASTIC, ROHS COMPLIANT, QFP-132 |
| 文件页数： | 27/109页 |
| 文件大小： | 787K |
| 代理商： | MC68332AMEH16 |
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MOTOROLA
MC68332
24
MC68332TS/D
When an external system clock signal is applied (i.e., the PLL is not used), duty cycle of the input is
critical, especially at near maximum operating frequencies. The relationship between clock signal duty
cycle and clock signal period is expressed:
Minimum external clock period =
minimum external clock high/low time
50% — percentage variation of external clock input duty cycle
3.3.2 Clock Synthesizer Operation
A voltage controlled oscillator (VCO) generates the system clock signal. A portion of the clock signal is
fed back to a divider/counter. The divider controls the frequency of one input to a phase comparator.
The other phase comparator input is a reference signal, either from the internal oscillator or from an
external source. The comparator generates a control signal proportional to the difference in phase be-
tween its two inputs. The signal is low-pass filtered and used to correct VCO output frequency.
The synthesizer locks when VCO frequency is identical to reference frequency. Lock time is affected by
the filter time constant and by the amount of difference between the two comparator inputs. Whenever
comparator input changes, the synthesizer must re-lock. Lock status is shown by the SLOCK bit in SYN-
CR.
The MCU does not come out of reset state until the synthesizer locks. Crystal type, characteristic fre-
quency, and layout of external oscillator circuitry affect lock time.
The low-pass filter requires an external low-leakage capacitor, typically 0.1
F, connected between the
XFC and VDDSYN pins.
VDDSYN is used to power the clock circuits. A separate power source increases MCU noise immunity
and can be used to run the clock when the MCU is powered down. Use a quiet power supply as the
VDDSYN source, since PLL stability depends on the VCO, which uses this supply. Place adequate ex-
ternal bypass capacitors as close as possible to the VDDSYN pin to ensure stable operating frequency.
When the clock synthesizer is used, control register SYNCR determines operating frequency and vari-
ous modes of operation. SYNCR can be read only when the processor is operating at the supervisor
privilege level.
The SYNCR X bit controls a divide by two prescaler that is not in the synthesizer feedback loop. Setting
X doubles clock speed without changing VCO speed. There is no VCO relock delay. The SYNCR W bit
controls a 3-bit prescaler in the feedback divider. Setting W increases VCO speed by a factor of four.
The SYNCR Y field determines the count modulus for a modulo 64 down counter, causing it to divide
by a value of Y
+ 1. When either W or Y value changes, there is a VCO relock delay.
Clock frequency is determined by SYNCR bit settings as follows:
FSYSTEM = FREFERENCE [4(Y + 1)(2
2W + X)]
In order for the device to perform correctly, the clock frequency selected by the W, X, and Y bits must
be within the limits specified for the MCU.
The VCO frequency is twice the system clock frequency if X = 1 or four times the system clock frequency
if X = 0.
The reset state of SYNCR ($3F00) produces a modulus-64 count.
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For More Information On This Product,
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相关代理商/技术参数 |
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|---|---|
| MC68332AMEH20 | 功能描述:32位微控制器 - MCU 32B MCU 2KRAM TPU QSM RoHS:否 制造商:Texas Instruments 核心:C28x 处理器系列:TMS320F28x 数据总线宽度:32 bit 最大时钟频率:90 MHz 程序存储器大小:64 KB 数据 RAM 大小:26 KB 片上 ADC:Yes 工作电源电压:2.97 V to 3.63 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:LQFP-80 安装风格:SMD/SMT |
| MC68332AMFC16 | 制造商:MOTOROLA 制造商全称:Motorola, Inc 功能描述:32-Bit Modular Microcontroller |
| MC68332AMFC20 | 制造商:Freescale Semiconductor 功能描述: |
| MC68332AMFV16 | 制造商:MOTOROLA 制造商全称:Motorola, Inc 功能描述:32-Bit Modular Microcontroller |
| MC68332AMFV20 | 制造商:MOTOROLA 制造商全称:Motorola, Inc 功能描述:32-Bit Modular Microcontroller |
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