MC912DG128ACPVE Datasheet, PDF (447/478 Pages) Freescale Semiconductor, Inc – Upward compatible with M68HC11 instruction set

Freescale Semiconductor, Inc.
Technical Data — MC68HC912DT128A
Section 23. Appendix: CGM Practical Aspects
23.1 Contents
23.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
23.3 Practical Aspects For The PLL Usage . . . . . . . . . . . . . . . . . .447
23.4 Printed Circuit Board Guidelines. . . . . . . . . . . . . . . . . . . . . . .453
23.2 Introduction
This sections provides useful and practical pieces of information
concerning the implementation of the CGM module.
23.3 Practical Aspects For The PLL Usage
23.3.1 Synthesized Bus Frequency
Starting from a ceramic resonator or quartz crystal frequency F_XTAL, if
‘refdv’ and ‘synr’ are the decimal content of the REFDV and SYNR
registers respectively, then the MCU bus frequency will simply be:
F_BUS
=
F_VCO
=
F----_{X----T----A----L----}⋅_---(_{---s--y----n---r----+----1----})
(refdv + 1)
synr ∈ {0,1,2,3...63}
refdv ∈ {0,1,2,3...7}
NOTE: It is not allowed to synthesize a bus frequency that is lower than the
crystal frequency, as the correct functioning of some internal
MC68HC912DT128A — Rev 4.0
MOTOROLA
Appendix: CGM Practical Aspects
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Technical Data
447