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 k
Ω
to 100 k
Ω
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
.
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
and
25 pF
*
Freescale Semiconductor, Inc...
EXTAL
MCU
XTAL
25 pF
*
10M
4xE
CRYSTAL
*
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
25 pF
*
EXTAL
FIRST
MCU
XTAL
25 pF
*
10M
4xE
CRYSTAL
220
EXTAL
NC OR
10 k – 100 k
LOAD
SECOND
MCU
XTAL
*
Values include all stray capacitances.
Figure 2-6 One Crystal Driving Two MCUs
PIN DESCRIPTIONS
2-4
For More Information On This Product,
Go to: www.freescale.com
MC68HC11F1
TECHNICAL DATA
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
