參數(shù)資料
型號: 9S12KT256DGV1
英文描述: MC9S12KT256 Device User Guide
中文描述: MC9S12KT256設(shè)備用戶指南
文件頁數(shù): 107/126頁
文件大?。?/td> 7307K
代理商: 9S12KT256DGV1
Device User Guide — 9S12KT256DGV1/D V01.09
107
Freescale Semiconductor
A.7.3 Phase Locked Loop
The oscillator provides the reference clock for the PLL. The PLL′s Voltage Controlled Oscillator (VCO)
is also the system clock source in self clock mode.
A.7.3.1 XFC Component Selection
This section describes the selection of the XFC components to achieve a good filter characteristics.
Figure A-3 Basic PLL functional diagram
The following procedure can be used to calculate the resistance and capacitance values using typical
values for K
1
, f
1
and i
ch
from
Table A-20
.
The grey boxes show the calculation for f
VCO
= 50MHz and f
ref
= 1MHz. E.g., these frequencies are used
for f
OSC
= 4MHz and a 25MHz bus clock.
The VCO Gain at the desired VCO frequency is approximated by:
f
f
(
)
K
1
1V
=
100
=
The phase detector relationship is given by:
2. Only valid if
full swing Pierce oscillator/external clock mode is selected
3. f
OSC
= 4MHz, C = 22pF.
4. Maximum value is for extreme cases using high Q, low frequency crystals
f
osc
1
refdv+1
f
ref
Phase
Detector
VCO
K
V
1
synr+1
f
vco
Loop Divider
K
Φ
1
2
f
cmp
C
s
R
C
p
VDDPLL
XFC Pin
K
V
K
1
e
-----------------------
e
60
---------------50
)
100
= -90.48MHz/V
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