68HC705SP7 datasheet(27/230 Pages) FREESCALE

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General Description

OSC1 and OSC2 Pins

MC68HC705JJ7/MC68HC705JP7 — Rev. 3.0

General Release Specification

General Description

The load capacitance values used in the oscillator circuit design should

include all stray capacitances. The ceramic resonator and components

should be mounted as close as possible to the pins for startup

stabilization and to minimize output distortion. An internal startup resistor

of approximately 2 M

Ω can be provided between OSC1 and OSC2 for

the ceramic resonator type oscillator by use of the OSCRES bit in the

MOR.

1.7.3 RC Oscillator

The lowest cost oscillator is the RC oscillator configuration where a

resistor is connected between the two oscillator pins as shown in Figure

1-3 (b). The internal startup resistor of approximately 2 M

Ω is not

recommended between OSC1 and OSC2 for the RC-type oscillator.

The selection of the RC oscillator configuration is done by product part

number selection as described in Section 17. Ordering Information.

1.7.4 External Clock

An external clock from another CMOS-compatible device can be

connected to the OSC1 input, with the OSC2 input not connected, as

shown in Figure 1-3 (c). This oscillator can be selected via software.

This configuration is possible regardless of whether the crystal/ceramic

resonator or RC oscillator configuration is used.

1.7.5 Internal Low-Power Oscillator

An internal low-power oscillator (LPO) is provided which is the default

oscillator out of reset. When operating from this internal LPO, the other

oscillator can be powered down by software to further conserve power.

The selection of the LPO configuration is done by product part number

selection as described in Section 17. Ordering Information.

Freescale Semiconductor, Inc.

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