MC68HC908GR4MP datasheet(24/286 Pages) FREESCALE

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General Description

MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

Freescale Semiconductor

1.5 Pin Functions

Descriptions of the pin functions are provided here.

1.5.1 Power Supply Pins (VDD and 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 1-5

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.

Figure 1-5. Power Supply Bypassing

1.5.2 Oscillator Pins (OSC1 and OSC2)

The OSC1 and OSC2 pins are the connections for the on-chip oscillator circuit. See Chapter 7 Clock

Generator Module (CGMC).

1.5.3 External Reset Pin (RST)

A logic 0 on the RST pin forces the MCU to a known startup state. RST is bidirectional, allowing a reset

of the entire system. It is driven low when any internal reset source is asserted. This pin contains an

internal pullup resistor that is always activated, even when the reset pin is pulled low. See Chapter 4

Resets and Interrupts.

1.5.4 External Interrupt Pin (IRQ)

IRQ is an asynchronous external interrupt pin. This pin contains an internal pullup resistor that is always

activated, even when the reset pin is pulled low. See Chapter 12 External Interrupt (IRQ).

1.5.5 CGM Power Supply Pins (VDDA and VSSA)

VDDA and VSSA are the power supply pins for the analog portion of the clock generator module (CGM).

Decoupling of these pins should be as per the digital supply. See Chapter 7 Clock Generator Module

(CGMC).

MCU

VDD

0.1

μF

VSS

VDD

NOTE: Component values shown represent typical applications.

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