TC1796
System Units (Vol. 1 of 2)
Clock System and Control
User’s Manual
3-13
V2.0, 2007-07
Clock, V2.0
N-Divider
The N-Divider in the feedback path of the PLL divides the VCO clock
f
VCO
by factor N for
the N-divider output clock
f
N
. This feedback clock is used as input clock for the PLL
phase detection unit, which compares it with the PLL input clock
f
P
. The phase detector
determines the difference between its two input clocks
f
P
and
f
N
and accordingly
regulates the frequency of the VCO output clock
f
VCO
.
shows the N factor values of the N-Divider which are selected by
programming the PLL_CLC.NDIV bit field. It also lists the resulting N-divider output clock
f
N
depending on N and dedicated VCO frequencies. Note that the N-Divider factor is
always PLL_CLC.NDIV+1. For proper operation of the PLL, only N-Divider values of 20
to 100 are allowed.
Table 3-3
N-Divider Selections
PLL_CLC.
NDIV
1)
1) These columns include decimal values.
N-Divider:
N = NDIV+1
Resulting
f
N
Frequency (in MHz) for
f
VCO
=
400 MHz
f
VCO
=
500 MHz
f
VCO
=
600 MHz
f
VCO
=
700 MHz
≤
18
≤
19
not allowed
19
20
20
25
30
35
20
21
19.05
23.81
28.57
33,33
21
22
18.18
22.73
27.27
31.82
…
…
…
…
…
...
97
98
4.08
5.10
6.12
7.14
98
99
4.04
5.05
6.06
7.07
99
2)
2) This is the default value after a power-on reset.
100
4
5
6
7
≥
100
≥
101
not allowed