MC68HC11F1_13 Datasheet, PDF (18/158 Pages) Freescale Semiconductor, Inc – Technical Data

Freescale Semiconductor, Inc.
The XTAL pin is normally left unterminated when an external CMOS compatible clock
is connected to the EXTAL pin. However, a 10 kΩ to 100 kΩ load resistor connected
from the XTAL output to ground can be used to reduce RFI noise emission.
The XTAL output is normally used to drive a crystal. The XTAL output can be buffered
with a high-impedance buffer, or it can be used to drive the EXTAL input of another
M68HC11 device. Refer to Figure 2-6.
In all cases, use caution when designing circuitry associated with the oscillator pins.
Load capacitances shown in the oscillator circuits include all stray layout capacitanc-
es. Refer to Figure 2-4, Figure 2-5, and Figure 2-6.
EXTAL
MCU
10M
XTAL
4xE
CRYSTAL
25 pF*
25 pF*
* ^{Values include all stray capacitances.}
Figure 2-4 Common Crystal Connections
EXTAL
MCU
XTAL
NC OR
10 k – 100 k
LOAD
CMOS-COMPATIBLE
EXTERNAL
OSCILLATOR
Figure 2-5 External Oscillator Connections
EXTAL
FIRST
MCU
10M
XTAL
4xE
CRYSTAL
25 pF*
25 pF*
220
NC OR
10 k – 100 k
LOAD
EXTAL
XTAL
SECOND
MCU
* ^{Values include all stray capacitances.}
Figure 2-6 One Crystal Driving Two MCUs
PIN DESCRIPTIONS
MC68HC11F1
2-4
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