Rev. D
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Page 18 of 56
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November 2008
ADSP-21367/ADSP-21368/ADSP-21369
shows core to CLKIN relationships with external oscil-
lator or crystal. The shaded divider/multiplier blocks denote
where clock ratios can be set through hardware or software
using the power management control register (PMCTL). For
more information, see the
ADSP-21368 SHARC Processor Hard-
ware Reference
and
Managing the Core PLL on Third-
Generation SHARC Processors (EE-290)
.
Use the exact timing information given. Do not attempt to
derive parameters from the addition or subtraction of others.
While addition or subtraction would yield meaningful results
for an individual device, the values given in this data sheet
reflect statistical variations and worst cases. Consequently, it is
not meaningful to add parameters to derive longer times. See
for voltage refer-
ence levels.
Note that in the user application, the PLL multiplier value
should be selected in such a way that the VCO frequency never
exceeds f
VCO
specified in
. The VCO frequency is calcu-
lated as follows:
f
VCO
= 2
×
PLLM
×
f
INPUT
where:
f
VCO
is the VCO frequency
PLLM
is the multiplier value programmed
f
INPUT
is the input frequency to the PLL in MHz.
f
INPUT
= CLKIN when the input divider is disabled
f
INPUT
= CLKIN
÷
2 when the input divider is enabled
Switching Characteristics
specify how the processor changes its
signals. Circuitry external to the processor must be designed for
compatibility with these signal characteristics. Switching char-
acteristics describe what the processor will do in a given
circumstance. Use switching characteristics to ensure that any
timing requirement of a device connected to the processor (such
as memory) is satisfied.
Timing Requirements
apply to signals that are controlled by cir-
cuitry external to the processor, such as the data input for a read
operation. Timing requirements guarantee that the processor
operates correctly with other devices.
Table 12. Clock Periods
Timing
Requirements
Description
1
t
CK
CLKIN Clock Period
t
CCLK
(Processor) Core Clock Period
t
PCLK
(Peripheral) Clock Period = 2 × t
CCLK
t
SCLK
Serial Port Clock Period = (t
CCLK
) × SR
t
SDCLK
SDRAM Clock Period = (t
CCLK
) × SDR
t
SPICLK
SPI Clock Period = (t
CCLK
) × SPIR
1
where:
SR = serial port-to-core clock ratio (wide range, determined by SPORT CLKDIV
bits in DIVx register)
SPIR = SPI-to-core clock ratio (wide range, determined by SPIBAUD register
setting)
SPICLK = SPI clock
SDR = SDRAM-to-core clock ratio (values determined by Bits 20–18 of the
PMCTL register)
Figure 4. Core Clock and System Clock Relationship to CLKIN
LOOP
FILTER
CLKIN
PCLK
S
DCLK
S
DRAM
DIVIDER
CLK_CFGx/
PMCTL
B
Y
P
A
S
S
M
U
X
DIVIDE
BY 2
PMCTL
CCLK
B
Y
P
A
S
S
M
U
X
PLL
XTAL
CLKIN
DIVIDER
RESETOUT
/
CLKOUT
RESET
PLL
MULTIPLIER
BUF
VCO
BUF
PLLI
CLK
PMCTL
PLL
DIVIDER
CLK_CFGx/PMCTL
P
IN
M
U
X
RESETOUT
CLKOUT
DELAY OF
4096 CLKIN
CYCLE
S
CORERST
PMCTL
CCLK
PCLK
CLK_CFGx/
PMCTL