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| 型號： | AM188ER-25KCW |
| 廠商： | ADVANCED MICRO DEVICES INC |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | CA-BAYONET |
| 中文描述： | 16-BIT, 25 MHz, MICROCONTROLLER, PQFP100 |
| 封裝： | PLASTIC, QFP-100 |
| 文件頁數(shù)： | 45/112頁 |
| 文件大?。?/td> | 2878K |
| 代理商： | AM188ER-25KCW |
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Am186
TM
ER and Am188
TM
ER Microcontrollers Data Sheet
45
DRAFT
Am186ER
Crystal-Driven Clock Source
The internal oscillator circuit of the Am186ER and
Am188ER microcontrollers is designed to function with
a parallel-resonant fundamental mode crystal. Be-
cause of the PLL, the crystal frequency can be twice,
equal to, or one quarter of the processor frequency. Do
not replace a crystal with an LC or RC equivalent. See
Figure 8 for a diagram of oscillator configurations.
The X1 and X2 signals are connected to an internal in-
verting amplifier (oscillator) that provides, along with
the external feedback loading, the necessary phase
shift. In such a positive feedback circuit, the inverting
amplifier has an output signal (X2) 180 degrees out of
phase of the input signal (X1).
The external feedback network provides an additional
180-degree phase shift. In an ideal system, the input to
X1 will have 360 or zero degrees of phase shift. The ex-
ternal feedback network is designed to be as close to
ideal as possible. If the feedback network is not provid-
ing necessary phase shift, negative feedback will
dampen the output of the amplifier and negatively af-
fect the operation of the clock generator. Values for the
loading on X1 and X2 must be chosen to provide the
necessary phase shift and crystal operation.
Selecting a Crystal
When selecting a crystal, the load capacitance should
always be specified (C
L
). This value can cause vari-
ance in the oscillation frequency from the desired spec-
ified value (resonance). The load capacitance and the
loading of the feedback network have the following re-
lationship:
where C
S
is the stray capacitance of the circuit. Placing
the crystal and C
L
in series across the inverting ampli-
fier and tuning these values (C
1
, C
2
) allows the crystal
to oscillate at resonance. Finally, there is a relationship
between C
1
and C
2
. To enhance the oscillation of the
inverting amplifier, these values need to be offset with
the larger load on the output (X2). Equal values of
these loads will tend to balance the poles of the invert-
ing amplifier.
The characteristics of the inverting amplifier set limits
on the following parameters for crystals:
ESR (Equivalent Series Resistance)60-ohm max
The recommended range of values for C
1
and C
2
are
as follows:
C
1
........................................ 15 pF
±
20%
C
2
........................................ 22 pF
±
20%
The specific values for C
1
and C
2
must be determined
by the designer and are dependent on the characteris-
tics of the chosen crystal and board design.
External Source Clock
Alternately, the internal oscillator can be driven by an
external clock source. The external clock source
should be connected to the input of the inverting ampli-
fier (X1) with the output (X2) left unconnected. X1 and
X2 are not 5-V tolerant and X1 has a maximum input
equal to V
CC
.
Figure 8.
Am186ER and Am188ER Microcontrollers Oscillator Configurations
(C
1
C
2
)
C
L
=
(
C
1
+
C
2
)+
C
S
Crystal
X1
b. Crystal Configuration
C
1
C
2
X2
To PLL
Oscillator
a. External Clock Configuration
Microcontroller
Am188ER/
X1
X2
To PLL
Oscillator
Microcontroller
Am188ER/
Am186ER
Notes:
X1 and X2 are not 5-V tolerant. The X1 maximum input is V
CC
.
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| AM188ER-25KI/W | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:16-Bit Microprocessor |
| AM188ER-25KIW | 制造商:Advanced Micro Devices 功能描述:MCU 16-bit E86 CISC ROMLess 3.3V 100-Pin PQFP 制造商:AMD (Advanced Micro Devices) 功能描述:MCU 16-bit E86 CISC ROMLess 3.3V 100-Pin PQFP |
| AM188ER-25VC/W | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:16-Bit Microprocessor |
| AM188ER-25VCW | 制造商:AMD 制造商全稱:Advanced Micro Devices 功能描述:High-Performance, 80C186- and 80C188-Compatible, 16-Bit Embedded Microcontrollers with RAM |
| AM188ER-25VD\\W | 制造商:Advanced Micro Devices 功能描述: |
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