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Clock Module
Freescale Semiconductor
8-3
8.1.1
Block Diagram
shows the clock module block diagram.
Figure 8-2. Clock Module Diagram
8.1.2
Features
Features of the clock module include:
•
16–66.66 MHz input clock frequency
•
Programmable frequency multiplication factor settings generating voltage-controlled oscillator
(VCO) frequencies from 300 – 540 MHz, resulting in a core frequency of 75 MHz (f
vco
4) to
266.67 MHz (maximum rated frequency).
•
Five user-programmable output dividers
— Each post-VCO divider can be programmed to divide-by-2 through divide-by-16. (There are
some dependencies of the divider settings. See
Section 8.2.1, “PLL Control Register (PCR)”
,
for details.) The post-VCO dividers can be enabled asynchronously or disabled via register.
— Allows glitch-free, dynamic switching of the output divider
•
Provides signals indicating when the PLL has acquired lock and lost lock
•
16 – 40 MHz reference crystal oscillator
•
Support for low-power modes
•
Direct clocking of system by input clock, bypassing the PLL
•
Loss-of-lock reset
•
Reference crystal oscillator for the real time clock (RTC) module. Input clock used is
programmable within the RTC.
Feedback Divider
(P)
Phase/Frequency
Detector (PFD)
Loop Filter
Voltage-Controlled
Oscillator (VCO)
Output Dividers
Output Clocks
Bus
Interface
VCO Clock
Frequency
Reset Config
Signals
PLL
Registers
OSC
EXTAL
XTAL
(
2 to
16)
Lock
Detect
External
Ref. Mode
OSC
To Real-Time
Clock
Crystal
Ref. Mode
EXTAL32K
XTAL32K
Содержание MCF54455
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