DCM driving multiple OBUF's ... skew in between ...

Hi all,

a simple question:

We intend to use a DCM in a Virtex-II Pro to drive multiple OBUF's but only ne feedback signal - of course. What is the best way to minimize the delay difference between the OBUF's?

Any help would be appreciated.

Markus

Reply to
Markus Meng
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Markus,

Keep the OBUFs to the right or left sides, and near the center of the parts (least H Clock Tree skew from IOB to IOB

Reply to
Austin Lesea

You may also want to use the DDR output flops in the IOB to output the clock rather than running them straight through a simple output buffer. This keeps the clocks on dedicated clock lines and eliminates a bunch of skew. There are several app-notes that show this, look at some of the DDR memory ones for examples.

Here's code a used to drive a clock out to some synchronous SRAM. Note by swapping the D0 and D1 values you can invert the clock.

// infer a DDR type I/O cell for low clock skew FDDRRSE uddr_clk( .Q (sram_clk), .C0 (g_sr_clk), .C1 (~g_sr_clk), .CE (1'b1), .D0 (1'b1), .D1 (1'b0), .R (1'b0), .S (1'b0) );

John Providenza

Reply to
John Providenza

John,

Youa re absolutely right! I failed to mention that you should always use the DDR FF for clock forwarding, as it has the best timing performance. Good catch.

Aust> You may also want to use the DDR output flops in the IOB to

Reply to
Austin Lesea

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