M68ICS08GR datasheet(108/408 Pages) FREESCALE

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Clock Generator Module (CGMC)

Technical Data

MC68HC908GR8 — Rev 4.0

108

Clock Generator Module (CGMC)

MOTOROLA

this table:

8. Select a VCO linear range multiplier, L, where fNOM = 38.4 kHz

9. Calculate and verify the adequacy of the VCO programmed

center-of-range frequency, fVRS. The center-of-range frequency is

the midpoint between the minimum and maximum frequencies

attainable by the PLL.

For proper operation,

10. Verify the choice of P, R, N, E, and L by comparing fVCLK to fVRS

and fVCLKDES. For proper operation, fVCLK must be within the

application’s tolerance of fVCLKDES, and fVRS must be as close as

possible to fVCLK.

NOTE:

Exceeding the recommended maximum bus frequency or VCO

frequency can crash the MCU.

11. Program the PLL registers accordingly:

a. In the PRE bits of the PLL control register (PCTL), program

the binary equivalent of P.

b. In the VPR bits of the PLL control register (PCTL), program

the binary equivalent of E.

Frequency Range

0 < fVCLK < 9,830,400

9,830,400

≤ f

VCLK < 19,660,800

19,660,800

≤ f

VCLK < 39,321,600

NOTE: Do not program E to a value of 3.

round

VCLK

NOM

--------------------------







VRS

()f

NOM

VRS

VCLK

–

NOM

--------------------------

≤

Freescale Semiconductor, Inc.

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