mc68hc908kx8 Freescale Semiconductor, Inc, mc68hc908kx8 Datasheet - Page 72

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

Internal Clock Generator Module (ICG)
The amplifier is enabled when the external clock generator enable (ECGEN) signal is set and when the
external crystal enable (EXTXTALEN) bit in the CONFIG (or MOR) register is set. ECGEN is controlled
by the clock enable circuit (see
is desired. When enabled, the amplifier will be connected between the PTB6/(OSC1) and
PTB7/(OSC2)/RST pins. Otherwise, the PTB7/(OSC2)/RST pin reverts to its port function. In its typical
configuration, the external oscillator requires five external components:
7.3.3.2 External Clock Input Path
The external clock input path is the means by which the microcontroller uses an external clock source.
The input to the path is the PTB6/(OSC1) pin and the output is the external clock (ECLK). The path, which
contains input buffering, is enabled when the external clock generator enable signal (ECGEN) is set.
When not enabled, the PTB6/(OSC1) pin reverts to its port function.
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•
•
•
•
•
Crystal, X
Fixed capacitor, C
Tuning capacitor, C
Feedback resistor, R
Series resistor, R
be required for all ranges of operation, especially with high frequency crystals. Refer to the crystal
manufacturer’s data for more information.)
1
NAME
NAME
EXTXTALEN
EXTSLOW
NAME
NAME
ECGEN
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
INTERNAL TO MCU
EXTERNAL
S
Figure 7-3. External Clock Generator Block Diagram
1
(included in the diagram to follow strict Pierce oscillator guidelines and may not
2
MODULE SIGNAL
REGISTER BIT
B
(can also be a fixed capacitor)
CONFIGURATION (OR MOR) BIT
TOP LEVEL SIGNAL
7.3.1 Clock Enable
GENERATOR
EXTERNAL
CLOCK
Circuit), and indicates that the external clock function
OSC1
PTB6
C
1
R
X
B
1
C
R
AMPLIFIER
2
S
*
INPUT PATH
OSC2
PTB7
These components are required
for external crystal use only.
*R
when used with higher-
frequency crystals. Refer
to manufacturer’s data.
S
can be 0 (shorted)
Freescale Semiconductor
ECLK