s908ey16g2vfar Freescale Semiconductor, Inc, s908ey16g2vfar Datasheet - Page 66

• Manufacturer Part Number: s908ey16g2vfar
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Configuration Registers (CONFIG1, CONFIG2, CONFIG3)
EXTSLOW — Slow External Crystal Enable Bit
EXTCLKEN — External Clock Enable Bit
TMBCLKSEL — Timebase Clock Select Bit
66
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 EXTSLOW bit has two functions. It configures the ICG module for a fast (1 MHz to 32 MHz) or
slow (30 kHz to 100 kHz) speed crystal. The option also configures the clock monitor operation in the
ICG module to expect an external frequency higher (307.2 kHz to 32 MHz) or lower (60 Hz to
307.2 kHz) than the base frequency of the internal oscillator. See
(ICG)
EXTCLKEN enables an external clock source or crystal/ceramic resonator to be used as a clock input.
Setting this bit enables PTC4/OSC1 pin to be a clock input pin. Clearing this bit (default setting) allows
the PTC4/OSC1 and PTC3/OSC2 pins to function as general-purpose input/output (I/O) pins. Refer to
Table 5-1
(ICG) Module
TMBCLKSEL enables an enable the extra divide by 128 prescaler in the timebase module. Setting this
bit enables the extra prescaler and clearing this bit disables it. Refer to
selection details.
1 = Allows PTC3/OSC2 to be an external crystal connection.
0 = PTC3/OSC2 functions as an I/O port pin (default).
1 = ICG set for slow external crystal operation
0 = ICG set for fast external crystal operation
1 = Allows PTC4/OSC1 to be an external clock connection
0 = PTC4/OSC1 and PTC3/OSC2 function as I/O port pins (default).
1 = Enables extra divide by 128 prescaler in timebase module.
0 = Disables extra divide by 128 prescaler in timebase module.
Module.
EXTCLKEN
for configuration options for the external source. See
Configuration Bits
0
0
1
1
External Clock
for a more detailed description of the external clock operation.
EXTXTALEN
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 1
0
1
0
1
Table 5-1. External Clock Option Settings
PTC4/OSC1
OSC1
OSC1
PTC4
PTC4
Pin Function
PTC3/OSC2
OSC2
PTC3
PTC3
PTC3
Chapter 8 Internal Clock Generator
Default setting — external
oscillator disabled
External oscillator disabled since
EXTCLKEN not set
External oscillator configured for
an external clock source input
(square wave) on OSC1
External oscillator configured for
an external crystal configuration
on OSC1 and OSC2. System will
also operate with square-wave
clock source in OSC1.
Chapter 8 Internal Clock Generator
Table 16-1
Description
Freescale Semiconductor
for timebase divider