MC68HC908KX8 Datasheet, PDF (145/310 Pages) Motorola, Inc – Microcontrollers

Configuration Register (CONFIG)
Functional Description
EXTCLKEN — External Clock Enable Bit
EXTCLKEN enables an external clock source or crystal/ceramic
resonator to be used as a clock input. Setting this bit enables
PTB6/(OSC1) pin to be a clock input pin. Clearing this bit (default
setting) allows the PTB6/(OSC1) and PTB7/(OSC2) pins to function
as a general-purpose input/output (I/O) pin. Refer to Table 9-1 for
configuration options for the external source. See Section 7. Internal
Clock Generator Module (ICG) for a more detailed description of the
external clock operation.
1 = Allows PTB6/(OSC1) to be an external clock connection
0 = PTB6/(OSC1) and PTB7/(OSC2) function as I/O port pins
(default).
EXTSLOW — Slow External Crystal Enable Bit
The EXTSLOW bit has two functions. It configures the ICG module for
a fast (1 MHz to 8 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 Section 7. Internal Clock Generator Module (ICG).
1 = ICG set for slow external crystal operation
0 = ICG set for fast external crystal operation
Table 9-1. External Clock Option Settings
External Clock
Configuration Bits
Pin Function
EXTCLKEN EXTXTALEN PTB6/(OSC1) PTB7/(OSC2)
Description
0
0
PTB6
PTB7
Default setting — external oscillator disabled
0
1
PTB6
PTB7
External oscillator disabled since EXTCLKEN
not set
1
0
OSC1
PTB7
External oscillator configured for an external
clock source input (square wave) on OSC1
External oscillator configured for an external
1
1
OSC1
OSC2
crystal configuration on OSC1 and OSC2.
System will also operate with square-wave
clock source in OSC1.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
MOTOROLA
Configuration Register (CONFIG)
Technical Data
145