MPC972 Просмотр технического описания (PDF) - Motorola => Freescale
Номер в каталоге
Компоненты Описание
производитель
MPC972 Datasheet PDF : 16 Pages
| |||
SYNC Output Description
In situations where output frequency relationships are not
integer multiples of each other there is a need for a signal for
system synchronization purposes. The SYNC output of the
MPC972 is designed to specifically address this need. The
MPC972 monitors the relationship between the Qa and the Qc
banks of outputs. It provides a low going pulse, one period in
duration, one period prior to the coincident rising edges of the
MPC972
Qa and Qc outputs. The duration and the placement of the
pulse is dependent on the higher of the Qa and Qc output
frequencies. The timing diagrams in the data sheet show the
various waveforms for the SYNC output. Note that the SYNC
output is defined for all possible combinations of the Qa and Qc
outputs even though under some relationships the lower
frequency clock could be used as a synchronizing signal.
1. Programmable Output Frequency Relationships (VCO_Sel = ‘1’)
fsela1
fsela0
Qa
fselb1
fselb0
Qb
fselc1
0
0
VCO/4
0
0
VCO/4
0
0
1
VCO/6
0
1
VCO/6
0
1
0
VCO/8
1
0
VCO/8
1
1
1
VCO/12
1
1
VCO/10
1
fselc0
0
1
0
1
Qc
VCO/2
VCO/4
VCO/6
VCO/8
2. Programmable Output Frequency Relationships (VCO_Sel = ‘1’)
fselFB2
fselFB1
fselFB0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
QFB
VCO/4
VCO/6
VCO/8
VCO/10
VCO/8
VCO/12
VCO/16
VCO/20
400
300
200
100
0
-100
-200
-300
-400
Qc3 Qc2 Qc1 Qc0 Qb3 Qb2 Qb1 Qb0 Qa3 Qa2 Qa1 Qa0
Figure 4. Typical Skews Relative to QFB
60
58
56
54
VCO/8
52
50
48
46
44
42
40
VCO/4
38
36
34
32
VCO/6
30
28
26
24
30 40 50 60 70 80 90 100 110
Reference Clock Frequency (MHz)
Figure 5. Typical Phase Jitter versus Reference Frequency
I/O Jitter
MOTOROLA
7
Share Link: 