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Clock Module
Freescale Semiconductor
8-11
PSR[LOCKS] status bit. LOLIRQ provides information to the lock detect logic to let it know if an interrupt
should be generated upon loss-of-lock. In PLL bypass mode, the PLL cannot lock; therefore, a loss-of-lock
condition cannot occur, and the LOLIRQ has no affect.
8.3.4
System Clock Modes
The system clock source is determined during reset. By default the PLL is placed in crystal-reference mode
and generates a core frequency of 10 times the input clock (internal bus 5x, FlexBus and USB clock 2.5x).
The BOOTMOD pins can override the default mode. See
Chapter 11, “Chip Configuration Module
for more information on default configuration, as well as overwriting these defaults during reset.
shows some of the various clocking scenarios offered on the processor. When the PCI controller
is enabled, the input reference clock bypasses the oscillator and become the PCI reference clock.
NOTE
If PCI is enabled, the input reference clock must be a bypass clock (external
oscillator) and must also equal the PCI operating frequency.
The PCI controller can operate at frequencies other than what is shown in
, but ensure that the
input bypass clock frequency is the PCI operating frequency. USB_CLKIN in the USB OTG column
indicates that the USB On-the-Go module receives its clock from the USB_CLKIN signal rather than the
PLL output.
Table 8-5. MCF54455 Clocking Scenarios (MHz)
ColdFire
Core
SDRAMC
(Core
2)
FlexBus
(Core
4)
PCI
USB OTG
Input Reference
Clock
Crystal Frequency
266.67
133.33
66.67
66.67
USB_CLKIN
66.67
—
1
1
When the PCI is enabled, use of a crystal oscillator is not supported.
266.67
133.33
66.67
33.33
USB_CLKIN
33.33
—
266.67
133.33
66.67
Disabled
USB_CLKIN
33.33, 66.67
33.33
240
120
60
60
60
60
240
120
60
30
60
30
240
120
60
Disabled
60
30, 60
20, 24, 30
200
100
50
66.67
USB_CLKIN
66.67
—
200
100
50
33.33
USB_CLKIN
33.33
—
200
100
50
Disabled
USB_CLKIN
33.33, 66.67
20, 25, 33.33
180
90
45
60
60
60
180
90
45
30
60
30
180
90
45
Disabled
60
30, 60
20, 24, 30
Содержание MCF54455
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