MC68HC08AS20 Datasheet, PDF (32/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

1.5.1 Power Supply Pins (V_DD and V_SS)
V_DD and V_SS are the power supply and ground pins. The MCU operates
from a single power supply.
Fast signal transitions on MCU pins place high, short-duration current
demands on the power supply. To prevent noise problems, take special
care to provide power supply bypassing at the MCU as Figure 1-3
shows. Place the C1 bypass capacitor as close to the MCU as possible.
Use a high-frequency-response ceramic capacitor for C1. C2 is an
optional bulk current bypass capacitor for use in applications that require
the port pins to source high current levels.
MCU
V_DD
V_SS
C1
0.1 µF
+
C2
V_DD
NOTE: Component values shown represent typical applications.
Figure 1-3. Power Supply Bypassing
V_SS is also the ground for the port output buffers and the ground return
for the serial clock in the serial peripheral interface module (SPI). (See
Section 18. Serial Peripheral Interface (SPI).)
NOTE: V_SS must be grounded for proper MCU operation.
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MC68HC08AS20 —Rev. 4.1
Freescale Semiconductor