MC68HC705MC4 Datasheet, PDF (12/99 Pages) Motorola, Inc – Microcontrollers

MC68HC705MC4 Specification Rev. 1.5
NOTE: A line over a signal name indicates an active low signal. For example,
RESET is active high and RESET is active low.
1.2 MASK OPTIONS
There is one user selectable option on the MC68HC705. This option is provided through
a bit within a Mask Option Register in the EPROM device, which is located and
programmed at $0F00 as part of the EPROM array. This option will be hard wired in the
ROM based device.
The normal state of this option and its alternate state are:
• COP Watchdog Timer Enabled. Option to Disable.
The ROM based device (MC68HC05MC4) will offer the following hard wired options:
• COP Watchdog Timer Enabled. Option to Disable.
• Stop Instruction Enabled. Option to Disable.
In the EPROM device, the STOP instruction will be disabled. These options are
compatible with the typical application environment in which the device is expected to be
used and will consequently allow the OTP devices to be used in production.
1.3 FUNCTIONAL PIN DESCRIPTION
The following paragraphs describe the functionality of each pin on the MC68HC705MC4
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. These pins are located close to each other for
low Electro Magnetic Interference (EMI) emissions.
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, OSC2
These pins provide control input for an on-chip clock oscillator circuit. A crystal, a ceramic
resonator or an external signal to these pins provides the system clock. The oscillator
frequency is two times the internal bus rate.
Section 1: Introduction
MOTOROLA
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