AN1746 View Datasheet(PDF) - Freescale Semiconductor

Part Name

Description

Manufacturer

AN1746

Migrating from the MC68HC705K1 to the MC68HC705KJ1

Freescale Semiconductor 

Clock

AN1746

Freescale Semiconductor, Inc.

Application Note

Migrating to the MC68HC705KJ1

The KJ1 has different clock circuitry than the K1. The main difference is

the RC clock option. The available clocking options on the KJ1 are listed

in Table 2.

Table 2. KJ1 Clock Options

Clock Option

Crystal oscillator

Crystal oscillator (32 kHz)

Ceramic resonator

RC oscillator

External clock

Comments

Internal feedback resistor

con gured in MOR

Do not use internal

feedback resistor

Internal feedback resistor

con gured in MOR

Uses either external or

internal resistor

Direct connection of clock

source

Part Number

MC68HC705KJ1

MC68HLC705KJ1

MC68HC705KJ1

MC68HRC705KJ1

MC68HC705KJ1

If you are using a crystal or ceramic resonator and want to use the

internal feedback resistor, the OSCRES bit in the mask option register

(MOR) must be set to 1. This enables the 2-MΩ feedback resistor. The

KJ1 has the option of using a 32-kHz crystal. Consult the KJ1 databook

about how to connect a 32-kHz crystal to the KJ1 properly.

The RC option on the KJ1 is quite different from the K1. The RC

oscillator has two options:

• For more accurate clocks, use an external resistor between the

OSC1 and OSC2 pins. Do not turn on the internal feedback

resistor. Make sure the OSCRES bit in the MOR is 0.

• For maximum cost reduction, the RC oscillator can utilize the

internal resistor and allow the chip to be driven with no external

components. This is also the least accurate way to clock the chip.

To use this option, make sure that the OSCRES bit in the MOR

is 1.

Like the K1, the KJ1 can be driven by an external clocking source also.

For More Information On This Product,

Go to: www.freescale.com

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