SYSTEM INTEGRATION MODULE MC68332
4-12 USER’S MANUAL
When the clock synthesizer is used, control register SYNCR determines operating fre-
quency and various modes of operation. The SYNCR W bit controls a three-bit pres-
caler in the feedback divider. Setting W increases VCO speed by a factor of four. The
SYNCR Y field determines the count modulus for a modulo 64 down counter, causing
it to divide by a value of Y + 1. When W or Y values change, VCO frequency changes,
and there is a VCO relock delay. The SYNCR X bit controls a divide-by-two circuit that
is not in the synthesizer feedback loop. When X = 0 (reset state), the divider is en-
abled, and system clock frequency is one-fourth VCO frequency; setting X disables
the divider, doubling clock speed without changing VCO speed. There is no relock de-
lay when clock speed is changed by the X bit.
Clock frequency is determined by SYNCR bit settings as follows:
The reset state of SYNCR ($3F00) produces a modulus-64 count.
For the device to perform correctly, system clock and VCO frequencies selected by
the W, X, and Y bits must be within the limits specified for the MCU. Do not use a com-
bination of bit values that selects either an operating frequency or a VCO frequency
greater than the maximum specified values in APPENDIX A ELECTRICAL CHARAC-
TERISTICS.
Table 4-7 shows clock control multipliers for all possible combinations of SYNCR bits.
Table 4-8 shows clock frequencies available with a 32.768-kHz reference and a max-
imum specified clock frequency of 20.97 MHz.
Table 4-7 Clock Control Multipliers
To obtain clock frequency in kilohertz, find counter modulus in the left column, then multiply reference frequency by value
in appropriate prescaler cell.
Modulus Prescalers
Y [W:X] = 00 [W:X] = 01 [W:X] = 10 [W:X] = 11
000000 4 8 16 32
000001 8 16 32 64
000010 12 24 48 96
011111 16 32 64 128
000011 20 40 80 160
000100 24 48 96 192
000101 28 56 112 224
000110 32 64 128 256
000111 36 72 144 288
001000 40 80 160 320
001001 44 88 176 352
001010 48 96 192 384
001011 52 104 208 416
001100 56 112 224 448
001101 60 120 240 480
001110 64 128 256 512
001111 68 136 272 544
010000 72 144 288 576
010001 76 152 304 608
F
SYSTEM
F
REFERENCE
4Y 1+()2
2W X+
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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