MC908JB16DWE Datasheet, PDF (34/332 Pages) Freescale Semiconductor, Inc – Microcontrollers

General Description
1.6 Pin Functions
Description of pin functions are provided here.
1.6.1 Power Supply Pins (V_DD, 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 bypass capacitors as close to the MCU power pins as
possible. Use high-frequency-response ceramic capacitors for C_BYPASS.
C_BULK are optional bulk current bypass capacitors for use in applications
that require the port pins to source high current levels.
MCU
V_DD
V_SS
C_BYPASS
0.1 µF
+
C_BULK
V_DD
NOTE: Values shown are typical values.
Figure 1-4. Power Supply Bypassing
1.6.2 Voltage Regulator Output Pin (V_REG)
V_REG is the 3.3V output of the on-chip voltage regulator. V_REG is used
internally for the MCU operation and the USB data driver. It is also used
to supply the voltage for the external pullup resistor required on the
USB’s D– line. The V_REG pin requires an external bulk capacitor 4.7µF
or larger and a 0.1µF ceramic bypass capacitor as Figure 1-5 shows.
Place the bypass capacitors as close to the V_REG pin as possible.
Technical Data
34
General Description
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor