MCMC68HC05L16 Freescale Semiconductor, Inc, MCMC68HC05L16 Datasheet - Page 17

• Manufacturer Part Number: MCMC68HC05L16
• Description: M68hc05 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

1.5.1 V
Power is supplied to the MCU through V
MCU operates from a single power supply. Very fast signal transitions occur on the MCU pins. The short
rise and fall times place very high short-duration current demands on the power supply. To prevent noise
problems, special care should be taken to provide good power supply bypassing at the MCU by using
bypass capacitors with good high-frequency characteristics that are positioned as close to the MCU as
possible. Bypassing requirements vary, depending on how heavily the MCU pins are loaded.
1.5.2 OSC1 and OSC2
The OSC1 and OSC2 pins are the connections for the 2-pin on-chip oscillator. The OSC1 and OSC2 pins
can accept:
The frequency, f
operating frequency, f
1.5.2.1 Crystal or Ceramic Resonator
The circuit in
The crystal manufacturer’s recommendations should be followed, as the crystal parameters determine
the external component values required to provide maximum stability and reliable startup. The load
capacitance values used in the oscillator circuit design should include all stray capacitances. The crystal
and components should be mounted as close as possible to the pins for startup stabilization and to
minimize output distortion. An internal startup feedback resistor of R
be selected as a mask option for MC68HC05L16. Typical R
Freescale Semiconductor
•
•
A crystal as shown in
An external clock signal as shown in
DD
and V
Figure
MASK OPTIONS
OSC
SS
, of the oscillator or external clock source is divided by 64 to produce the internal
1-3(a) shows a typical 2-pin oscillator circuit for an AT-cut, parallel resonant crystal.
OP
, by default.
(a) Crystal Connections
Figure
MC68HC05L16 • MC68HC705L16 Data Sheet, Rev. 4.1
Figure 1-3. Oscillator Connections
1-3(a)
OSC1
C
4 MHz (TYP)
O1
DD
MCU
R
OF
and V
Figure
C
OSC2
O2
SS
1-3(b)
. V
DD
is the positive supply, and V
OF
resistor value is 5.5 MΩ.
OSC1
Source Connection
OF
(b) External Clock
between OSC1 and OSC2 may
MCU
EXTERNAL CLOCK
UNCONNECTED
OSC2
Functional Pin Description
SS
is ground. The
17