MC68HC(7)08KH12Rev. 1.1 Advance Information
Freescale Semiconductor 29
1.5.2 Power Supply Pins (VDDA, VSSA, VDD1, VSS1, VDD2, and VSS2)
VDDA and VSSA are the analog power supply and ground pins used by
the on-chip Phase-Locked Loop circuit.
VDD2 and VSS2 are the power supply and ground pins used by the
internal circuitry of the chip.
VDD1 and VSS1 are the power supply and ground pins to the I/O pads.
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 1-3
shows. Place the bypass capacitors as close to the MCU power pins as
possible. Use high-frequency-response ceramic capacitors for CBYPASS.
CBULK are optional bulk current bypass capacitors for use in applications
that require the port pins to source high current levels.
Figure 1-3. Power Supply Bypassing
MCU
CBULK
CBYPASS
10nF
VSS1
+
NOTE: Values shown are typical values.
VDD2
CBYPASS
10nF
VDD2
CBYPASS
10nF
VSS2
VSSA
VDDA
Vbus