15-8
ADSP-2126x SHARC Processor Hardware Reference
When using an external crystal, the maximum crystal frequency cannot
exceed 25 MHz. The internal clock generator, when used in conjunction
with the
XTAL
pin and an external crystal, is designed to support up to a
maximum of 25 MHz external crystal frequency. For all other external
clock sources, the maximum
CLKIN
frequency is 50 MHz.
shows the internal core clock switching frequency across a
range of
CLKIN
frequencies. The minimum operational range for any given
frequency is constrained by the operating range of the PLL. Note that the
goal in selecting a particular clock ratio for the processor application is to
provide the highest internal frequency, given a
CLKIN
frequency.
If an external master clock is used, it should not drive the
CLKIN
pin when
the processor is not powered. The clock must be driven immediately after
power-up—otherwise, internal gates stay in an undefined (hot) state and
can draw excess current. After power-up, there should be sufficient time
for the oscillator to start up, reach full amplitude, and deliver a stable
CLKIN
signal to the processor before the reset is released. This may take
Table 15-3. Clock Rate Ratios After Reset (Default)
CLKCFG[1-0]
Core to CLKIN Ratio
00
3:1, PLLD = 2, PLLM = 6
01
16:1, PLLD = 2, PLLM = 32
10
8:1, PLLD = 2, PLLM = 16
11
Reserved
Table 15-4. PLL Multiplier and Divider Settings
PLLD[7:6]
PLL Divider Ratio
PLLM[5:0]
PLL Multiplier Ratio
00 (= reset)
Clock Divider = 2
000000
Clock Multiplier = 64
01
Clock Divider = 4
000001
Clock Multiplier = 1
10
Clock Divider = 8
...
...
11
Clock Divider = 16
111111
Clock Multiplier = 63
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 ...