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Clock Module
Freescale Semiconductor
8-7
Table 8-3. PCR Field Descriptions
Field
Description
31–24
PFDR
Feedback divider for setting the VCO frequency. Valid values range from 4 (0x4) to 34 (0x22). Other settings are
invalid and stable operation is not guaranteed. The reset value depends on the selected chip configuration. See
Chapter 11, “Chip Configuration Module (CCM),”
for more information.
Eqn. 8-1
where
f
REF
is the PLL input frequency from the internal oscillator or EXTAL clock source (defined by the selected
chip configuration).
23–20
Reserved, must be cleared.
19–16
OUTDIV5
Output divider for generating the USB clock frequency. The divider is the value of this bit field plus 1. The reset value
depends on the selected chip configuration. See
Chapter 11, “Chip Configuration Module (CCM),”
for more
information. A value of zero disables this clock.
Note:
The OUTDIV5 resulting frequency must be 60 MHz if used as the USB clock source.
Eqn. 8-2
15–12
OUTDIV4
Output divider for generating the PCI clock frequency. The divider is the value of this bit field plus 1. The reset value
depends on the selected chip configuration. See
Chapter 11, “Chip Configuration Module (CCM),”
for more
information. A value of zero disables this clock.
Eqn. 8-3
11–8
OUTDIV3
Output divider for generating the FlexBus clock (FB_CLK) frequency. The divider is the value of this bit field plus 1.
The reset value depends on the selected chip configuration. See
Chapter 11, “Chip Configuration Module (CCM),”
for more information. A value of zero disables this clock.
Note:
The OUTDIV3 divider value must be four or eight times the OUTDIV1 divider. For example, if OUTDIV1 equals
0001, then OUTDIV3 must equal 0111 or 1111. FB_CLK must also not exceed 66 MHz.
Eqn. 8-4
f
VCO
f
REF
PFDR
=
f
USB
f
VCO
OUTDIV5 1
+
-------------------------------------
=
f
PCI
f
VCO
OUTDIV4 1
+
-------------------------------------
=
f
FB_CLK
f
SYS
4 or 8
--------------
f
VCO
OUTDIV3 1
+
-------------------------------------
=
=
Содержание MCF54455
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