R
Virtex™-II Platform FPGAs: Detailed Description
PHASE_SHIFT in fixed mode is limited to 255, and in
variable mode it is limited to 128.
•
If PERIOD
≤ 0.5 * FINE_SHIFT_RANGE, then
CLKIN
PHASE_SHIFT is limited to 255 in either mode.
Operating Modes
The frequency ranges of DCM input and output clocks
depend on the operating mode specified, either
low-frequency mode or high-frequency mode, according to
Table 22. (For actual values, see Virtex-II Switching Char-
acteristics in Module 3). The CLK2X, CLK2X180, CLK90,
and CLK270 outputs are not available in high-frequency
mode.
High or low-frequency mode is selected by an attribute.
Table 22: DCM Frequency Ranges
Low-Frequency Mode
High-Frequency Mode
Output Clock
CLK0, CLK180
CLKIN Input
CLK Output
CLKIN Input
CLK Output
CLKIN_FREQ_DLL_LF CLKOUT_FREQ_1X_LF CLKIN_FREQ_DLL_HF CLKOUT_FREQ_1X_HF
CLK90, CLK270
CLK2X, CLK2X180
CLKDV
CLKIN_FREQ_DLL_LF CLKOUT_FREQ_1X_LF
CLKIN_FREQ_DLL_LF CLKOUT_FREQ_2X_LF
NA
NA
NA
NA
CLKIN_FREQ_DLL_LF CLKOUT_FREQ_DV_LF CLKIN_FREQ_DLL_HF CLKOUT_FREQ_DV_HF
CLKFX, CLKFX180
CLKIN_FREQ_FX_LF
CLKOUT_FREQ_FX_LF CLKIN_FREQ_FX_HF
CLKOUT_FREQ_FX_HF
Locations/Organization
Virtex-II DCMs are placed on the top and bottom of each
block RAM and multiplier column. The number of DCMs
depends on the device size, as shown in Table 23.
Table 23: DCM Organization
Device
XC2V40
Columns
DCMs
2
2
4
4
4
4
4
6
6
6
6
4
4
XC2V80
XC2V250
XC2V500
XC2V1000
XC2V1500
XC2V2000
XC2V3000
XC2V4000
XC2V6000
XC2V8000
8
8
8
8
8
12
12
12
12
DS031-2 (v3.0) August 1, 2003
Product Specification
www.xilinx.com
1-800-255-7778
Module 2 of 4
32
XILINX [ XILINX, INC ]
