MC68HC705P6A Datasheet, PDF (22/130 Pages) Motorola, Inc – HCMOS Microcontroller Unit

General Description
1.4 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.
1.4.1 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.
1.4.2 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.
Advance Information
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General Description
MC68HC705P6A — Rev. 2.0
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