MC68HC08GZ32 Datasheet, PDF (60/320 Pages) Freescale Semiconductor, Inc – Microcontrollers

Clock Generator Module (CGM)
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
OSCSTOPENB
(FROM CONFIG)
OSC1
RB
X1
C₁
CGMXCLK
OSC2
CGMXFC
RS
R_F1
C_F2
C_F1
C₂
V_SSA
V_DDA
V_DD
CBYP
Note: Filter network in box can be replaced with a single capacitor, but will degrade stability.
Figure 4-2. CGM External Connections
4.4 I/O Signals
The following paragraphs describe the CGM I/O signals.
4.4.1 Crystal Amplifier Input Pin (OSC1)
The OSC1 pin is an input to the crystal oscillator amplifier.
MC68HC08GZ32 Data Sheet, Rev. 3
60
Freescale Semiconductor