MC705P6ACPE Datasheet, PDF (15/98 Pages) Freescale Semiconductor, Inc – M68HC05 Microcontrollers

Functional Pin Description
1.3 Functional Pin Description
The following paragraphs describe the functionality of each pin on the MC68HC705P6A package. Pins
connected to subsystems described in other chapters provide a reference to the chapter instead of a
detailed functional description.
1.3.1 V_DD and V_SS
Power is supplied to the MCU through V_DD and V_SS. V_DD is connected to a regulated +5 volt supply and
V_SS is connected to ground.
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, take special care to
provide good power supply bypassing at the MCU. Use bypass capacitors with good high-frequency
characteristics and position them as close to the MCU as possible. Bypassing requirements vary,
depending on how heavily the MCU pins are loaded.
1.3.2 OSC1 and OSC2
The OSC1 and OSC2 pins are the control connections for the on-chip oscillator. The OSC1 and OSC2
pins can accept the following:
1. A crystal as shown in Figure 1-2(a)
2. A ceramic resonator as shown in Figure 1-2(a)
3. An external clock signal as shown in Figure 1-2(b)
The frequency, f_osc, of the oscillator or external clock source is divided by two to produce the internal bus
clock operating frequency, f_op. The oscillator cannot be turned off by software unless the MOR bit, SWAIT,
is clear when a STOP instruction is executed.
To V_DD (or STOP)
MCU
To V_DD (or STOP)
MCU
OSC1
4.7 MΩ
OSC2
OSC1
OSC2
UNCONNECTED
EXTERNAL CLOCK
37 pF
37 pF
(a) Crystal or Ceramic
Resonator Connections
(b) External Clock Source
Connections
Figure 1-2. Oscillator Connections
MC68HC705P6A Advance Information Data Sheet, Rev. 2.1
Freescale Semiconductor
15