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:
FSYSTEM = FREFERENCE[4(Y + 1)(22W + X)]
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.
4
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
Y
Prescalers
[W:X] = 00
[W:X] = 01
8
[W:X] = 10
16
[W:X] = 11
32
000000
000001
000010
011111
000011
000100
000101
000110
000111
001000
001001
001010
001011
001100
001101
001110
001111
010000
010001
010010
010011
4
8
16
32
64
12
16
20
24
28
32
36
40
44
48
52
56
60
64
68
72
76
80
84
24
48
96
32
64
128
160
192
224
256
288
320
352
384
416
448
480
512
544
576
608
640
672
40
80
48
96
56
112
128
144
160
176
192
208
224
240
256
272
288
304
320
336
64
72
80
88
96
104
112
120
128
136
144
152
160
168
MOTOROLA
4-12
SYSTEM INTEGRATION MODULE
MC68331
USER’S MANUAL
MOTOROLA [ MOTOROLA ]
