MC68HCP11A1MP2(1996) View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

MC68HCP11A1MP2
(Rev.:1996)

HCMOS Single-Chip Microcontroller

Motorola => Freescale 

2 SIGNAL DESCRIPTIONS AND OPERATING MODES

The signal descriptions and operating modes are presented in this section. When the

microcontroller is in an expanded multiplexed operating mode, 18 pins change func-

tion to support a multiplexed address/data bus.

2.1 Signal Pin Descriptions

The following paragraphs provide a description of the input/output signals. Reference

is made, where applicable, to other sections that contain more detail about the function

being performed.

2.1.1 Input Power (VDD) and Ground (VSS)

Power is supplied to the microcontroller using these pins. VDD is the positive power in-

put and VSS is ground. Although the MC68HC11A8 is a CMOS device, very fast signal

transitions are present on many of its pins. Short rise and fall times are present even

when the microcontroller is operating at slow clock rates. Special care must be taken

to provide good power supply bypassing at the MCU. Recommended bypassing would

include a 0.1 µF ceramic capacitor between the VDD and VSS pins and physically adja-

cent to one of the two pins. A bulk capacitance, whose size depends on the other cir-

cuitry in the system, should also be present on the circuit board.

2

2.1.2 Reset (RESET)

This active low bidirectional control signal is used as an input to initialize the

MC68HC11A8 to a known start-up state, and as an open-drain output to indicate that

an internal failure has been detected in either the clock monitor or computer operating

properly (COP) watchdog circuit. This reset signal is significantly different from the re-

set signal used on other Motorola MCUs. Please refer to 9 RESETS, INTERRUPTS,

AND LOW POWER MODES before designing circuitry to generate or monitor this sig-

nal.

2.1.3 Crystal Driver and External Clock Input (XTAL, EXTAL)

These two pins provide the interface for either a crystal or a CMOS compatible clock

to control the internal clock generator circuitry. The frequency applied to these pins

shall be four times higher than the desired E clock rate. The XTAL pin is normally left

unterminated when using an external CMOS compatible clock input to the EXTAL pin.

However, a 10K to 100K load resistor to ground may be used to reduce RFI noise

emission. The XTAL output is normally intended to drive only a crystal.

The XTAL output may be buffered with a high-input-impedance buffer such as the

74HC04, or it may be used to drive the EXTAL input of another M68HC11.

In all cases take extra care in the circuit board layout around the oscillator pins. Load

capacitances shown in the oscillator circuits include all stray layout capacitances. Re-

fer to Figure 2-1, Figure 2-2, and Figure 2-3 for diagrams of oscillator circuits.

MC68HC11A8

TECHNICAL DATA

SIGNAL DESCRIPTIONS AND OPERATING MODES

MOTOROLA

2-1

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