
General Description
MC68HC08LK60 MC68HC908LK60 Advance Information Data Sheet, Rev. 1.1
20
Freescale Semiconductor
1.3.1 Power Supply Pins (VDD, VSS, EVDD, and EVSS)
The two VDD and two VSS pins are power supply and ground pins for the digital sections of the MCU. The
MCU operates from a single-power supply ranging from 2 volts (
±10%) to 3 volts (±10%).
The EVDD and EVSS pins are power supply and ground pins for the I/O section of the MCU.
Very fast signal transitions on the MCU pins place high, short-duration current demands on the power
supply. To prevent noise problems, take special care to provide good power supply bypassing at the MCU
as shown in
Figure 1-2. 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.
EVSS pin is also the ground return pin for the serial clock in the serial peripheral interface module (SPI).
It enables the user to implement a coplanar transmission line for the SPI clock on printed circuit boards
(PCBs) with no ground plane. EVSS can help reduce radiated radio frequency (RF) emissions by
Figure 1-2. Power Supply Bypassing
NOTE
Component values shown represent typical applications.
1.3.2 Oscillator Pins (OSC1 and OSC2)
The OSC1 and OSC2 pins are the crystal connections for the on-chip oscillator.
Figure 1-3 shows a typical
crystal oscillator circuit for a parallel resonant crystal. Follow the crystal supplier’s recommendations, as
the crystal parameters determine the external component values required to provide reliable startup and
maximum stability. The load capacitance values used in the oscillator circuit design should include all
stray layout capacitances. To minimize output distortion and radio frequency (RF) emissions, mount the
crystal and capacitors as close as possible to the pins. Pay special attention to minimizing the length of
the oscillator load capacitors’ ground return path.
MCU
VDD
C2
C1
0.1
F
VSS
VDD
+