XC2VP20-6FF1152C Xilinx, Inc., XC2VP20-6FF1152C Datasheet - Page 46

• Manufacturer Part Number: XC2VP20-6FF1152C
• Description: Pro Platform FPGA
• Manufacturer: Xilinx, Inc.

Functional Description: FPGA
Table 21: DCM Status Pins
Clock De-skew
The DCM de-skews the output clocks relative to the input
clock by automatically adjusting a digital delay line. Addi-
tional delay is introduced so that clock edges arrive at inter-
nal registers and block RAMs simultaneously with the clock
edges arriving at the input clock pad. Alternatively, external
clocks, which are also de-skewed relative to the input clock,
can be generated for board-level routing. All DCM output
clocks are phase-aligned to CLK0 and, therefore, are also
phase-aligned to the input clock.
To achieve clock de-skew, the CLKFB input must be con-
nected, and its source must be either CLK0 or CLK2X. Note
that CLKFB must always be connected, unless only the
CLKFX or CLKFX180 outputs are used and de-skew is not
required.
Frequency Synthesis
The DCM provides flexible methods for generating new
clock frequencies. Each method has a different operating
frequency range and different AC characteristics. The
CLK2X and CLK2X180 outputs double the clock frequency.
The CLKDV output creates divided output clocks with divi-
sion options of 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5,
8, 9, 10, 11, 12, 13, 14, 15, and 16.
The CLKFX and CLKFX180 outputs can be used to pro-
duce clocks at the following frequency:
where M and D are two integers. Specifications for M and D
are provided under
M = 4 and D = 1, which results in a clock output frequency
four times faster than the clock input frequency (CLKIN).
CLK2X180 is phase shifted 180 degrees relative to CLK2X.
CLKFX180 is phase shifted 180 degrees relative to CLKFX.
46
FREQ
Status Pin
0
1
2
3
4
5
6
7
CLKFX
DCM Timing
=
M D
Phase Shift Overflow
Parameters. By default,
CLKFX Stopped
CLKIN Stopped
FREQ
Function
N/A
N/A
N/A
N/A
N/A
CLKIN
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All frequency synthesis outputs automatically have 50/50
duty cycles, with the exception of the CLKDV output when
performing a non-integer divide in high-frequency mode.
See
Note that CLK2X and CLK2X180 are not available in
high-frequency mode.
Table 22: CLKDV Duty Cycle for Non-integer Divides
Phase Shifting
The DCM provides additional control over clock skew
through either coarse or fine-grained phase shifting. The
CLK0, CLK90, CLK180, and CLK270 outputs are each
phase shifted by ¼ of the input clock period relative to each
other, providing coarse phase control. Note that CLK90 and
CLK270 are not available in high-frequency mode.
Fine-phase adjustment affects all nine DCM output clocks.
When activated, the phase shift between the rising edges of
CLKIN and CLKFB is a specified fraction of the input clock
period.
In variable mode, the
dynamically incremented or decremented as determined by
PSINCDEC synchronously to PSCLK, when the PSEN
input is active.
shifting. For more information on DCM features, see the
Virtex-II Pro User Guide.
Table 23
variable mode.
Table 23: Fine Phase Shifting Control Pins
PSINCDEC
PSEN
PSCLK
PSDONE
Control Pin
Table 22
CLKDV_DIVIDE
lists fine-phase shifting control pins, when used in
for more details.
1.5
2.5
3.5
4.5
5.5
6.5
7.5
Figure 51
Direction
Out
In
In
In
PHASE_SHIFT
illustrates the effects of fine-phase
DS083-2 (v1.0) January 31, 2002
Advance Product Specification
Increment or decrement
Enable ± phase shift
Clock for phase shift
Active when completed
Duty Cycle
value can also be
Function
5 / 11
6 / 13
7 / 15
2 / 5
3 / 7
4 / 9
1/ 3
R