MC908GZ60CFUE Datasheet, PDF (80/352 Pages) Freescale Semiconductor, Inc – Standard features, Features of the CPU08

Clock Generator Module (CGM)
4.3.9 CGM External Connections
In its typical configuration, the CGM requires external components. Five of these are for the crystal
oscillator and two or four are for the PLL.
The crystal oscillator is normally connected in a Pierce oscillator configuration, as shown in Figure 4-2.
Figure 4-2 shows only the logical representation of the internal components and may not represent actual
circuitry. The oscillator configuration uses five components:
• Crystal, X₁
• Fixed capacitor, C₁
• Tuning capacitor, C₂ (can also be a fixed capacitor)
• Feedback resistor, R_B
• Series resistor, R_S
The series resistor (R_S) is included in the diagram to follow strict Pierce oscillator guidelines. Refer to the
crystal manufacturer’s data for more information regarding values for C1 and C2.
Figure 4-2 also shows the external components for the PLL:
• Bypass capacitor, C_BYP
• Filter network
Routing should be done with great care to minimize signal cross talk and noise.
SIMOSCEN
OSCENINSTOP
(FROM CONFIG)
CGMXCLK
OSC1
R_B
X1
C₁
OSC2
R_S
C₂
CGMXFC
R_F1
C_F2
C_F1
V_SSA
V_DDA
V_DD
C_BYP
Note: Filter network in box can be replaced with a single capacitor, but will degrade stability.
Figure 4-2. CGM External Connections
MC68HC908GZ60 • MC68HC908GZ48 • MC68HC908GZ32 Data Sheet, Rev. 6
80
Freescale Semiconductor