Motorola ColdFire MCF5281 - Manual (Page 182)

Clock Module
9-12 Freescale Semiconductor
The RFD is not in the feedback loop of the PLL, so changing the RFD divisor does not affect PLL
operation.
Figure 9-5 shows the external support circuitry for the crystal oscillator with example component values.
Actual component values depend on crystal specifications.
The following subsections describe each major block of the PLL. Refer to Figure to see how these
functional sub-blocks interact.
Figure 9-5. Crystal Oscillator Example
9.7.4.1 Phase and Frequency Detector (PFD)
The PFD is a dual-latch phase-frequency detector. It compares both the phase and frequency of the
reference and feedback clocks. The reference clock comes from either the crystal oscillator or an external
clock source.
V
SS
V
SSSYN
EXTAL XTAL
RS
RF
C1 C2
ON-CHIP
8-MHz CRYSTAL CONFIGURATIO
C1 = C2 = 16 pF
RF = 1 M
Ω
RS = 470
Ω
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3