Datasheet

General Description
Technical Data MC68HC908LJ12 — Rev. 2.1
40 General Description Freescale Semiconductor
1.6 Pin Functions
Description of pin functions are provided here.
1.6.1 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 1-4
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. V
SS
must be grounded for
proper MCU operation.
1.6.2 Analog Power Supply Pin (V
DDA
)
V
DDA
is the voltage supply for the analog parts of the MCU. Connect the
V
DDA
pin to the same voltage potential as V
DD
. For maximum noise
immunity, route V
DDA
via a separate trace and place bypass capacitors
as close as possible to the package (see Figure 1-4).
Figure 1-4. Power Supply Bypassing
MCU
V
DD
C2(a)
C1(a)
0.1 µF
V
SS
V
DD
+
NOTE: Component values shown
represent typical applications.
V
DDA
C2(b)
C1(b)
0.1 µF
+
V
DD