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Phase Locked Loop and Clock Control
20-6
ADSP-BF537 Blackfin Processor Hardware Reference
As long as the
MSEL
and
DF
control bits in the PLL control register
(
PLL_CTL
) remain constant, the PLL is locked.
L
If changing the clock ratio via writing a new
SSEL
value into
PLL_DIV
, take care that the enabled peripherals do not suffer data
loss due to
SCLK
frequency changes.
When changing clock frequencies in the PLL, the PLL requires time to
stabilize and lock to the new frequency. The PLL lock count register
(
PLL_LOCKCNT
) defines the number of
SCLK
cycles that occur before the
processor sets the
PLL_LOCKED
bit in the
PLL_STAT
register. When execut-
ing the PLL programming sequence, the internal PLL lock counter begins
incrementing upon execution of the
IDLE
instruction. The lock counter
increments by 1 each
SCLK
cycle. When the lock counter has incremented
to the value defined in the
PLL_LOCKCNT
register, the
PLL_LOCKED
bit is set.
Table 20-3. System Clock Ratio
Signal Name
SSEL[3:0]
Divider Ratio
VCO/SCLK
Example Frequency Ratios (MHz)
VCO
SCLK
0000 Reserved
N/A
N/A
0001 1:1
100
100
0010
2:1
200
100
0011
3:1
400
133
0100
4:1
500
125
0101
5:1
600
120
0110
6:1
600
100
N = 7–15
N:1
600
600/N
Содержание Blackfin ADSP-BF537
Страница 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...