MOTOROLA
Chapter 9. Clocks and Power Control
9-5
Part III. The Hardware Interface
9.3 External Clock Inputs
The input clock source to the PLL is an external clock oscillator at the bus frequency. The
PLL skew elimination between the CLOCKIN pin and the internal bus clock is guaranteed.
9.4 Main PLL
The main PLL performs frequency multiplication and skew elimination. It allows the
processor to operate at a high internal clock frequency using a low-frequency clock input,
which has two immediate beneÞts: A lower clock input frequency reduces overall
electromagnetic interference generated by the system, and oscillating at different
frequencies eliminates the need for another oscillator to the system.
9.4.1 PLL Block Diagram
Figure 9-1 shows how clocking is implemented and the interdependencies of the SCMR
Þelds:
¥
BUSDFÑ60x bus division factor
¥
CPMDFÑCPM division factor. This value is always 1.
¥
PLLDFÑPLL pre-divider value. Ensures that PLLMF is an integer value regardless
of whether CPM_CLK/CLKIN is an integer.
¥
PLLMFÑPLL multiplication factor
These Þelds are described in detail in Table 9-5.
Figure 9-1. System PLL Block Diagram
The reference signal (CLKIN) goes to the phase comparator that controls the direction (up
or down) that the charge pump drives the voltage across the external Þlter capacitor (XFC).
÷ (PLLDF + 1)
VCO_OUT
´
2
(PLLMF + 1)
÷ (CPMDF + 1)
÷ (BUSDF + 1)
÷ 4
2
2 (DFBRG + 1)
CPM_CLK
CPM_CLK_90°
BUS_CLK (= CLKIN)
BUS_CLK_90°
SCC_CLK
SCC_CLK_90°
BRG
CLKIN
(÷2)
PLLDF ensures that PLLMF is an integer, according to the
following formula:
PLLMF =
CPM_CLK
CLKIN
´
(PLLDF + 1) Ð 1
General-Purpose Divider
(2*CPM_CLK)
Summary of Contents for MPC8260 PowerQUICC II
Page 1: ...MPC8260UM D 4 1999 Rev 0 MPC8260 PowerQUICC II UserÕs Manual ª ª ...
Page 66: ...lxvi MPC8260 PowerQUICC II UserÕs Manual MOTOROLA ...
Page 88: ...1 18 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part I Overview ...
Page 120: ...2 32 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part I Overview ...
Page 138: ...Part II iv MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part II Configuration and Reset ...
Page 184: ...4 46 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part II ConÞguration and Reset ...
Page 202: ...Part III vi MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part III The Hardware Interface ...
Page 266: ...8 34 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part III The Hardware Interface ...
Page 382: ...10 106 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part III The Hardware Interface ...
Page 392: ...11 10 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part III The Hardware Interface ...
Page 430: ...Part IV viii MOTOROLA Part IV Communications Processor Module ...
Page 490: ...14 36 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part IV Communications Processor Module ...
Page 524: ...17 10 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Part IV Communications Processor Module ...
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Page 980: ...A 4 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA Appendixes ...
Page 1002: ...Index 22 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA INDEX ...
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