MC68HC05SU3A Datasheet, PDF (21/80 Pages) Freescale Semiconductor, Inc – Fully static chip design featuring the industry standard 8-bit M68HC05 core

Freescale Semiconductor, Inc.
MCU
MCU
2
OSC1
OSC2
OSC1
OSC2
10MΩ
Unconnected
External Clock
25p
25p
(a) Crystal or ceramic resonator connections
MCU
V_DD
OSC1
OSC2
R
Unconnected
(c) RC option 1 - external resistor
(b) External clock source connection
MCU
OSC1
OSC2
(d) RC option 2 - internal resistor
Figure 2-1 Oscillator Connections
2.2.1 Crystal Oscillator
The circuit in Figure 2-1(a) shows a typical oscillator circuit for an AT-cut, parallel resonant crystal.
The crystal manufacturer’s recommendations should be followed, as the crystal parameters
determine the external component values required to provide maximum stability and reliable
start-up. The load capacitance values used in the oscillator circuit design should include all stray
capacitances. The crystal and components should be mounted as close as possible to the pins for
start-up stabilization and to minimize output distortion. An external start-up resistor of
approximately 10MΩ is needed between OSC1 and OSC2 for the crystal type oscillator.
2.2.2 External Clock
An external clock from another CMOS-compatible device can be connected to the OSC1 input,
with the OSC2 input not connected, as shown in Figure 2-1(b).
TPG
MC68HC05SU3A
PIN DESCRIPTIONS
For More Information On This Product,
2-3
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