Texas Instruments TMS320C6726 사용자 설명서
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4.17 External Clock Input From Oscillator or CLKIN Pin
OSCV
DD
C
5
C
7
C
8
X
1
R
S
R
B
OSCIN
OSCOUT
C
6
OSCV
SS
CLKIN
Clock
Input
From
From
OSCIN
to
PLL
On-Chip 1.2-V Oscillator
(a)
External 3.3-V LVCMOS-Compatible Clock Source
(b)
OSCV
DD
OSCIN
OSCOUT
OSCV
SS
CLKIN
Clock
Input
From
From
CLKIN
to
PLL
CV
DD
(1.2 V)
NC
TMS320C6727, TMS320C6726, TMS320C6722
Floating-Point Digital Signal Processors
Floating-Point Digital Signal Processors
SPRS268E – MAY 2005 – REVISED JANUARY 2007
The C672x device includes two choices to provide an external clock input, which is fed to the on-chip PLL
to generate high-frequency system clocks. These options are illustrated in
to generate high-frequency system clocks. These options are illustrated in
•
(a) illustrates the option that uses an on-chip 1.2-V oscillator with external crystal circuit.
•
(b) illustrates the option that uses an external 3.3-V LVCMOS-compatible clock input with
the CLKIN pin.
Note that the two clock inputs are logically combined internally before the PLL so the clock input that is not
used must be tied to ground.
used must be tied to ground.
Figure 4-42. C672x Clock Input Options
If the on-chip oscillator is chosen, then the recommended component values for
(a) are listed
in
Table 4-38. Recommended On-Chip Oscillator Components
FREQUENCY
XTAL TYPE
X
1
C
5
(1)
C
6
(1)
C
7
C
8
R
B
R
S
22.579
AT-49
KDS 1AF225796A
470 pF
470 pF
8 pF
8 pF
1 M
Ω
0
Ω
22.579
SMD-49
KDS 1AS225796AG
470 pF
470 pF
8 pF
8 pF
1 M
Ω
0
Ω
24.576
AT-49
KDS 1AF245766AAA
470 pF
470 pF
8 pF
8 pF
1 M
Ω
0
Ω
24.576
SMD-49
KDS 1AS245766AHA
470 pF
470 pF
8 pF
8 pF
1 M
Ω
0
Ω
(1)
Capacitors C
5
and C
6
are used to reduce oscillator jitter, but are optional. If C
5
and C
6
are not used, then the node connecting
capacitors C
7
and C
8
should be tied to OSCV
SS
and OSCV
DD
should be tied to CV
DD
.
100
Peripheral and Electrical Specifications