ADSP-BF537 Blackfin Processor Hardware Reference
20-5
Dynamic Power Management
Core Clock/System Clock Ratio Control
describes the programmable relationship between the
VCO
fre-
quency and the core clock.
shows the relationship of the
VCO
frequency to the system clock. Note the divider ratio must be chosen to
limit the
SCLK
to a frequency specified in the processor data sheet. The
SCLK
drives all synchronous, system-level logic.
The divider ratio control bits,
CSEL
and
SSEL
, are in the PLL divide regis-
ter (
PLL_DIV
). For information about this register, see
.
The reset value of
CSEL[1:0]
is 0x0, and the reset value of
SSEL[3:0]
is
0x5. These values can be reprogrammed at startup by the boot code.
By writing the appropriate value to
PLL_DIV
, you can change the
CSEL
and
SSEL
value dynamically. Note the divider ratio of the core clock can never
be greater than the divider ratio of the system clock. If the
PLL_DIV
register
is programmed to illegal values, the
SCLK
divider is automatically increased
to be greater than or equal to the core clock divider.
Unlike writing the
PLL_CTL
register, the
PLL_DIV
register can be pro-
grammed at any time to change the
CCLK
and
SCLK
divide values without
entering the idle state.
Table 20-2. Core Clock Ratio
Signal Name
CSEL[1:0]
Divider Ratio
VCO/CCLK
Example Frequency Ratios (MHz)
VCO
CCLK
00 1
300
300
01 2
600
300
10
4
600
150
11
8
400
50
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...