M68HC08 datasheet(34/332 Pages) FREESCALE

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General Description

Technical Data

MC68HC908JB16 — Rev. 1.1

General Description

Freescale Semiconductor

1.6 Pin Functions

Description of pin functions are provided here.

1.6.1 Power Supply Pins (VDD, VSS)

VDD and VSS 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 1-4

shows. Place the bypass capacitors as close to the MCU power pins as

possible. Use high-frequency-response ceramic capacitors for CBYPASS.

CBULK are optional bulk current bypass capacitors for use in applications

that require the port pins to source high current levels.

Figure 1-4. Power Supply Bypassing

1.6.2 Voltage Regulator Output Pin (VREG)

VREG is the 3.3V output of the on-chip voltage regulator. VREG is used

internally for the MCU operation and the USB data driver. It is also used

to supply the voltage for the external pullup resistor required on the

USB’s D– line. The VREG pin requires an external bulk capacitor 4.7µF

or larger and a 0.1

µF ceramic bypass capacitor as Figure 1-5 shows.

Place the bypass capacitors as close to the VREG pin as possible.

MCU

CBULK

CBYPASS

0.1 µF

NOTE: Values shown are typical values.

VDD

VSS

M68HC08 Datasheet(PDF) 34 Page - Freescale Semiconductor, Inc