Pin Assignments
1.4.1 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 shown in
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
NOTE
V
SS
must be grounded for proper MCU operation.
1.4.2 Oscillator Pins (OSC1 and OSC2)
The OSC1 and OSC2 pins are the connections for the on-chip oscillator circuit. See
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
for more information.
1.4.4 External Interrupt Pin (IRQ)
IRQ is an asynchronous external interrupt pin. See
1.4.5 Analog Power Supply Pin (V
DDA
)
V
DDA
is the power supply pin for the analog portion of the Clock Generator Module (CGM). See
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
23
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
