DLL usage, multiple clock domains on FPGA.

T

Tolgay Akkaya

Guest
I am targeting a Spartan IIE (400E) device with four global clock
buffers (BUFG) and four DLL's.

But I need five clock domains 25MHz(clkin, DLL1), 50MHz (clk2x, DLL1)
and 30MHz (clkdv, DLL2), 60MHz (clkin, DLL2), 120MHz (clk2x, DLL2) in my
design.

I know that it is not allowed to use more than 2 BUFG per DLL.

I would like to use the DLL's to have a zero propagation delay and low
clock skew between output clock signals distributed throughout the
device. The primary global nets are driven by global buffers (25, 50, 60
and 120 MHz).

The 30 MHz clock domain is not so critical, so maybe I can use a
secondary global nets for this clock domain?

How can I drive the secondary global nets with an output of the DLL e.g.
the 30 MHz without using a BUFG?
 

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