Datasheet

MC68HC912D60A — Rev. 3.1 Technical Data
Freescale Semiconductor Appendix: CGM Practical Aspects 427
Technical Data — MC68HC912D60A
Section 21. Appendix: CGM Practical Aspects
21.1 Contents
21.2 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .427
21.3 Practical Aspects For The PLL Usage . . . . . . . . . . . . . . . . . .427
21.4 Printed Circuit Board Guidelines. . . . . . . . . . . . . . . . . . . . . . .433
21.2 Introduction
This sections provides useful and practical pieces of information
concerning the implementation of the CGM module.
21.3 Practical Aspects For The PLL Usage
21.3.1 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:
NOTE: It is not allowed to synthesize a bus frequency that is lower than the
crystal frequency, as the correct functioning of some internal
F
BUS
F
VCO
F
XTAL
synr 1+()⋅
refdv 1+()
------------------------------------------------==
synr 0,1,2,3...63}{∈
refdv 0,1,2,3...7}{∈