MC68HC908GR8 Datasheet, PDF (24/286 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

General Description
1.5 Pin Functions
Descriptions of the pin functions are provided here.
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 1-5
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.
MCU
V_DD
V_SS
C1
0.1 μF
+
C2
V_DD
NOTE: Component values shown represent typical applications.
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 (V_DDA and V_SSA)
V_DDA and V_SSA 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).
MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7
24
Freescale Semiconductor