General Description
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
22 Freescale Semiconductor
1.4.1 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 1-4
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 1-4. Power Supply Bypassing
1.4.2 Oscillator Pins (OSC1 and OSC2)
The OSC1 and OSC2 pins are the connections for the on-chip oscillator circuit. For more detailed
information, see Chapter 4 Clock Generator Module (CGM).
1.4.3 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. See Chapter 14 System
Integration Module (SIM).
1.4.4 External Interrupt Pin (IRQ)
IRQ is an asynchronous external interrupt pin. See Chapter 8 External Interrupt (IRQ).
1.4.5 CGM Power Supply Pins (VDDA and VSSAD)
VDDA and VSSAD are the power supply pins for the analog portion of the clock generator module (CGM).
Decoupling of these pins should be per the digital supply. See Chapter 4 Clock Generator Module (CGM).
MCU
VDD
C2
C1
0.1 µF
VSS
VDD
+
Note: Component values shown represent typical applications.
1–10 µF