ADSP-2126x SHARC Processor Hardware Reference
13-3
Precision Clock Generator
Clock Outputs
As stated in the overview, each of the two units (A and B) produces a clock
output and a frame sync output. The clock output is derived from the
input to the PCG with a 20-bit divisor.
If the divisor is either zero or one, the PCG’s clock generation unit is
bypassed, and the clock input is connected directly to the clock output.
Otherwise, the PCG unit clock output frequency is equal to the input
clock frequency, divided by a 20-bit integer. The integer is specified in the
CLKADIV
bit field (bits 19–0 of the
PCG_CTLA_1
register) for unit A and a
corresponding bit field in the
PCG_CTLB_1
register for unit B. See also
and
.
The clock outputs have two other control bits that enable the A and B
units,
ENCLKA
and
ENCLKB
, respectively (bits 31 of the
PCG_CTLA_0
and
PCG_CTLB_0
registers). These bits enable (= 1) and disable (= 0) the clock
output signal for units A and B, respectively. When disabled, clock output
is held at logic low.
The
CLKASOURCE
bit (bit 31 in the
PCG_CTLA_1
register) specifies the input
source for the clock of unit A. When this bit is cleared (= 0), the input is
sourced from the external oscillator, as shown in
. When set
(= 1), the input is sourced from the SRU, as specified in the
SRU_CLK3
register in
PCG_EXTA_I
(bits 4–0). See
.
The PCG unit B functions identically, except that the
PCG_CTLB_1
bit (bit
31) indicates that the external source for unit B is specified in
PCG_EXTB_I
(bits 9–5 of the
SRU_CLK3
register). See
.
Note that the clock output is always set (as closely as possible) to a 50%
duty cycle. If the clock divisor is even, the duty cycle of the clock output is
exactly 50%. If the clock divisor is odd, then the duty cycle is slightly less
Frequency of Clock Output
=
Frequency of Clock Input
Clock Divisor
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...