mc68hc908kx8 Freescale Semiconductor, Inc, mc68hc908kx8 Datasheet - Page 48

• Manufacturer Part Number: mc68hc908kx8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Configuration Register (CONFIG)
EXTCLKEN — External Clock Enable Bit
EXTSLOW — Slow External Crystal Enable Bit
EXTXTALEN — External Crystal Enable Bit
48
EXTCLKEN
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)/RST pins to function as a general-purpose input/output (I/O) pin.
Refer to
Generator Module (ICG)
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
(ICG).
EXTXTALEN enables the external oscillator circuits to be configured for a crystal configuration where
the PTB6/(OSC1) and PTB7/(OSC2)/RST pins are the connections for an external crystal.
Configuration Bits
0
0
1
1
1 = Allows PTB6/(OSC1) to be an external clock connection
0 = PTB6/(OSC1) and PTB7/(OSC2)/RST function as I/O port pins (default).
1 = ICG set for slow external crystal operation
0 = ICG set for fast external crystal operation
External Clock
Other Resets:
Table 4-1
Address:
EXTXTALEN
Reset:
This bit does not function without setting the EXTCLKEN bit also.
Read:
Write:
0
1
0
1
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
1. The LVI5OR3 bit is cleared only by a power-on reset (POR).
U = Unaffected
for configuration options for the external source. See
COPRS
$001F
Bit 7
0
0
Figure 4-2. Configuration Register 1 (CONFIG1)
PTB6/(OSC1)
for a more detailed description of the external clock operation.
OSC1
OSC1
Table 4-1. External Clock Option Settings
PTB6
PTB6
LVISTOP
6
0
0
Pin Function
LVIRSTD
PTB7/(OSC2)/RST
5
0
0
OSC2
PTB7
PTB7
PTB7
NOTE
LVIPWRD
4
0
0
Chapter 7 Internal Clock Generator Module
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.
LVI5OR3
U
3
0
(1)
SSREC
2
0
0
Chapter 7 Internal Clock
Description
STOP
1
0
0
Freescale Semiconductor
COPD
Bit 0
0
0