5-3
CLOCK GENERATION AND POWER MANAGEMENT
Choose C
1
and L
1
component values in the third overtone crystal circuit to satisfy the following
conditions:
•
The LC components form an equivalent series resonant circuit at a frequency below the
fundamental frequency. This criterion makes the circuit inductive at the fundamental
frequency. The inductive circuit cannot make the 90° phase shift and oscillations do not
take place.
•
The LC components form an equivalent parallel resonant circuit at a frequency about
halfway between the fundamental frequency and the third overtone frequency. This
criterion makes the circuit capacitive at the third overtone frequency, necessary for oscil-
lation.
•
The two capacitors and inductor at OSCOUT, plus some stray capacitance, approximately
equal the 20 pF load capacitor, C
X2
, used alone in the fundamental mode circuit.
Figure 5-3. Crystal Connections to Microprocessor
Choosing C
1
as 200 pF (at least 10 times the value of the load capacitor) simplifies the circuit
analysis. At the series resonance, the capacitance connected to L
1
is 200 pF in series with 20 pF.
The equivalent capacitance is still about 20 pF and the equation in Figure 5-4(a) yields the series
resonant frequency.
To examine the parallel resonant frequency, refer to Figure 5-3(c), an equivalent circuit to Figure
5-3(b). The capacitance connected to L
1
is 200 pF in parallel with 20 pF. The equivalent capaci-
tance is still about 200 pF (within 10%) and the equation in Figure 5-4(a) now yields the parallel
resonant frequency.
CLKIN
OSCOUT
(a)
Fundamental
Mode Circuit
CLKIN
OSCOUT
(b)
Third Overtone
Mode Circuit
C
X2
C
X1
C
X2
C
X1
L
1
(c)
Third Overtone Mode
(Equivalent Circuit)
C
X2
L
1
C1
C
X1
= C
X2
C
1
L
1
= 20pF
= 200pF
= (See text)
A1126-0A
Содержание 80C186EA
Страница 1: ...80C186EA 80C188EA Microprocessor User s Manual...
Страница 2: ...80C186EA 80C188EA Microprocessor User s Manual 1995...
Страница 19: ......
Страница 20: ...1 Introduction...
Страница 21: ......
Страница 28: ...2 Overview of the 80C186 Family Architecture...
Страница 29: ......
Страница 79: ......
Страница 80: ...3 Bus Interface Unit...
Страница 81: ......
Страница 129: ......
Страница 130: ...4 Peripheral Control Block...
Страница 131: ......
Страница 139: ......
Страница 140: ...5 ClockGenerationand Power Management...
Страница 141: ......
Страница 165: ......
Страница 166: ...6 Chip Select Unit...
Страница 167: ......
Страница 190: ...7 Refresh Control Unit...
Страница 191: ......
Страница 205: ......
Страница 206: ...8 Interrupt Control Unit...
Страница 207: ......
Страница 239: ...INTERRUPT CONTROL UNIT 8 32...
Страница 240: ...9 Timer Counter Unit...
Страница 241: ......
Страница 265: ......
Страница 266: ...10 Direct Memory Access Unit...
Страница 267: ......
Страница 295: ...DIRECT MEMORY ACCESS UNIT 10 28...
Страница 296: ...11 Math Coprocessing...
Страница 297: ......
Страница 314: ...12 ONCE Mode...
Страница 315: ......
Страница 318: ...A 80C186 Instruction Set Additions and Extensions...
Страница 319: ......
Страница 330: ...B Input Synchronization...
Страница 331: ......
Страница 334: ...C Instruction Set Descriptions...
Страница 335: ......
Страница 383: ...INSTRUCTION SET DESCRIPTIONS C 48...
Страница 384: ...D Instruction Set Opcodes and Clock Cycles...
Страница 385: ......
Страница 408: ...Index...
Страница 409: ......