68HC05CL48 datasheet(17/145 Pages) MOTOROLA

17 / 145 page

June 11, 1997

GENERAL RELEASE SPECIFICATION

MC68HC05CL48

GENERAL DESCRIPTION

MOTOROLA

REV 2.0

1-5

1.4

SIGNAL DESCRIPTION

The following paragraphs give a description of the general function of each pin.

1.4.1 VDD and VSS

Power is supplied to the MCU through V

DD and VSS pins. VDD is connected to a

regulated positive supply and V

SS is connected to ground. These pins are located

close to each other for low EMI, Electro Magnetic Interference, emission.

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.

Figure 1-3. Power Supply Decoupling

1.4.2 RESET

This pin can be used as an input to reset the MCU to a known start-up state by

pulling it to the low state. The RESET pin contains a steering diode to discharge

any voltage on the pin to VDD, when the power is removed. The RESET pin

contains an internal Schmitt trigger to improve its noise immunity as an input. The

RESET pin has an internal pulldown device that pulls the RESET pin low when

there is an internal COP Watchdog reset or during the power-on reset cycles.

Refer to Section 5.

1.4.3 IRQ

This pin has an option in the option register that provides two different choices of

interrupt triggering sensitivity. The IRQ pin contains an internal Schmitt trigger as

part of its input to improve noise immunity. Refer to Section 4.

VDD

VSS

0.47uF (Ceramic)

1uF

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