mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 574

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Appendix A Electrical Characteristics
A.3.3
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.3.3.1
This section describes the selection of the XFC components to achieve a good filter characteristics.
The following procedure can be used to calculate the resistance and capacitance values using typical values
for K
The grey boxes show the calculation for f
for f
The VCO Gain at the desired VCO frequency is approximated by:
The phase detector relationship is given by:
i
574
ch
is the current in tracking mode.
OSC
1
, f
1
= 4MHz and a 25MHz bus clock.
f
and i
osc
Phase Locked Loop
XFC Component Selection
ch
from
refdv+1
1
Table
K
V
=
A-13.
f
ref
K
1
VDDPLL
Figure A-2. Basic PLL Functional Diagram
e
K
--------------------------- -
f 1 f vco
K 1 1V
MC9S12E256 Data Sheet, Rev. 1.08
=
–
–
VCO
f
cmp
i
ch
C
p
C
= 50MHz and f
=
s
Detector
K
Loop Divider
Phase
–
V
100
synr+1
K
1
R
= 316.7Hz/
e
----------------------- -
60 50
–
100
–
ref
= 1MHz. E.g., these frequencies are used
XFC Pin
= -90.48MHz/V
1
2
VCO
K
V
Freescale Semiconductor
f
vco