Virtex-E 1.8 V Field Programmable Gate Arrays
R
DS022-2 (v3.0) March 21, 2014
Module 2 of 4
Production Product Specification
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Useful Application Examples
The Virtex-E DLL can be used in a variety of creative and
useful applications. The following examples show some of
the more common applications. The Verilog and VHDL
example files are available at:
ftp://ftp.xilinx.com/pub/applications/xapp/xapp132.zip
Standard Usage
The circuit shown in
Figure 27 resembles the BUFGDLL
macro implemented to provide access to the RST and
LOCKED pins of the CLKDLL.
Board Level Deskew of Multiple Non-Virtex-E
Devices
The circuit shown in
Figure 28 can be used to deskew a
system clock between a Virtex-E chip and other non-Vir-
tex-E chips on the same board. This application is com-
monly used when the Virtex-E device is used in conjunction
with other standard products such as SRAM or DRAM
devices. While designing the board level route, ensure that
the return net delay to the source equals the delay to the
other chips involved.
Board-level deskew is not required for low-fanout clock net-
works. It is recommended for systems that have fanout lim-
itations on the clock network, or if the clock distribution chip
cannot handle the load.
Do not use the DLL output clock signals until after activation
of the LOCKED signal. Prior to the activation of the
LOCKED signal, the DLL output clocks are not valid and
can exhibit glitches, spikes, or other spurious movement.
The dll_mirror_1 files in the xapp132.zip file show the
VHDL and Verilog implementation of this circuit.
Deskew of Clock and Its 2x Multiple
The circuit shown in
Figure 29 implements a 2x clock multi-
plier and also uses the CLK0 clock output with a zero ns
skew between registers on the same chip. Alternatively, a
clock divider circuit can be implemented using similar con-
nections.
Figure 27: Standard DLL Implementation
CLK0
CLK90
CLK180
CLK270
CLK2X
CLKDV
LOCKED
CLKIN
CLKFB
RST
ds022_028_121099
CLKDLL
BUFG
IBUFG
IBUF
OBUF
Figure 28: DLL Deskew of Board Level Clock
Figure 29: DLL Deskew of Clock and 2x Multiple
ds022_029_121099
CLK0
CLK90
CLK180
CLK270
CLK2X
CLKDV
LOCKED
CLKIN
CLKFB
RST
CLKDLL
OBUF
IBUFG
CLK0
CLK90
CLK180
CLK270
CLK2X
CLKDV
LOCKED
CLKIN
CLKFB
RST
CLKDLL
BUFG
IBUFG
Non-Virtex-E Chip
Other Non_Virtex-E Chips
Virtex-E Device
CLK0
CLK90
CLK180
CLK270
CLK2X
CLKDV
LOCKED
CLKIN
CLKFB
RST
ds022_030_121099
CLKDLL
BUFG
IBUFG
IBUF
OBUF
BUFG