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Internal Clock Generator (ICG) Module
Functional Description
MC68HC908GT16 MC68HC908GT8 — Rev. 2
Technical Data
MOTOROLA
Internal Clock Generator (ICG) Module
117
7.4.3 External Clock Generator
The ICG also provides for an external oscillator or external clock source,
if desired. The external clock generator, shown in Figure 7-3, contains
an external oscillator amplifier and an external clock input path.
Figure 7-3. External Clock Generator Block Diagram
7.4.3.1 External Oscillator Amplifier
The external oscillator amplifier provides the gain required by an
external crystal connected in a Pierce oscillator configuration. The
amount of this gain is controlled by the slow external (EXTSLOW) bit in
the CONFIG2 register. When EXTSLOW is set, the amplifier gain is
reduced for operating low-frequency crystals (32 kHz to 100 kHz). When
EXTSLOW is clear, the amplifier gain will be sufficient for 1-MHz to 8-
MHz crystals. EXTSLOW must be configured correctly for the given
crystal or the circuit may not operate.
C1
C2
RB
X1