MC68HC908GT16 Datasheet, PDF (137/412 Pages) Motorola, Inc – Microcontrollers

Internal Clock Generator (ICG) Module
CONFIG2 Options
7.7.2 External Crystal Enable (EXTXTALEN)
External crystal enable (EXTXTALEN), when set, will enable an amplifier
to drive the PTE3/OSC2 pin from the PTE4/OSC1 pin. The amplifier will
drive only if the external clock enable (EXTCLKEN) bit and the ECGON
bit are also set. If EXTCLKEN or ECGON are clear, PTE3/OSC2 will
perform the PTE3 function. When EXTXTALEN is clear, PTE3/OSC2 will
always perform the PTE3 function.
EXTXTALEN, when set, also configures the clock monitor to expect an
external clock source in the valid range of crystals (30 kHz to 100 kHz or
1 MHz to 8 MHz). When EXTXTALEN is clear, the clock monitor will
expect an external clock source in the valid range for externally
generated clocks when using the clock monitor (60 Hz to 32 MHz).
EXTXTALEN, when set, also configures the external clock stabilization
divider in the clock monitor for a 4096 cycle timeout to allow the proper
stabilization time for a crystal. When EXTXTALEN is clear, the
stabilization divider is configured to 16 cycles since an external clock
source does not need a startup time.
The default state for this option is clear.
7.7.3 Slow External Clock (EXTSLOW)
Slow external clock (EXTSLOW), when set, will decrease the drive
strength of the oscillator amplifier, enabling low-frequency crystal
operation (30 kHz–100 kHz) if properly enabled with the external clock
enable (EXTCLKEN) and external crystal enable (EXTXTALEN) bits.
When clear, EXTSLOW enables high-frequency crystal operation
(1 MHz to 8 MHz).
EXTSLOW, when set, also configures the clock monitor to expect an
external clock source that is slower than the low-frequency base clock
(60 Hz to 307.2 kHz). When EXTSLOW is clear, the clock monitor will
expect an external clock faster than the low-frequency base clock
(307.2 kHz to 32 MHz).
The default state for this option is clear.
MC68HC908GT16 • MC68HC908GT8 — Rev. 2
MOTOROLA
Internal Clock Generator (ICG) Module
Technical Data
137