MAC7200 datasheet(525/976 Pages) FREESCALE

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Initialization/Application Information

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

447

24.5

Initialization/Application Information

If the oscillator is used in External Clock mode, the XTAL pin should be grounded.

24.6

OSC Bus Aborts

There is no bus interface for the oscillator. All oscillator control registers reside in the CRG module.

24.7

OSC Differences from MAC71xx

•

No Reduced Oscillator Amplitude (ROA) mode

•

EXTAL and XTAL changed from 2.5V to 3.3V signals

•

Colpitts mode removed

•

Frequency range for loop controlled Pierce mode changed

•

Frequency range for external clock mode changed

24.8

OSC Application Usage

24.8.1

OSC Mode Selection

The oscillator mode is chosen by the value of the XCLKS hardware configuration pin at reset, as follows:

NOTE

Unlike the rest of the hardware configuration pins, the XCLKS pin is not

latched during every system reset. It is only latched during a Power On

Reset or during a reset after a loss of clock has occurred.

24.8.2

OSC Mode - ALC Mode (XCLKS = 1)

In this mode, the Oscillator reference clock is fed by the oscillator. Refer to Figure 24-4.

Table 24-2. Oscillator Modes

XCLKS

Mode

External Clock Mode. In this mode, the EXTAL pin drives the Oscillator

reference clock directly.

ALC Mode. In this mode, the EXTAL signal is inverted and fed back out

to the crystal (via XTAL). The Oscillator reference clock is driven by the

oscillator.

MAC7200 Datasheet(PDF) 525 Page - Freescale Semiconductor, Inc

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