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DCM.

Hi, there

I am creating a project with Spartan 3 board. and wanna add DCM into the XPS 6.2 project under menu "project- add/edit cores(dialog)"

What I want is to get the clock down to clock/2. There are 3 moduls in the DCM, I am using the digital frenquency synthesizer (DFS).

I added 3 ports: "clkin", "rst" as input, "clkfx" as output in the internal ports connections, didnot add anything into the external ports connections.

connected the "clkin" to "sys_clk"=50mMHz of the external ports, reconnected the clock input ports of other components who HAD "sys_clk" as input to the output port "clkfx"

the parameters I have c_clkfx_multiply = 1 c_clkfx_divide = 2 c_clkin_period = 40.000000

Reply to
im.de
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I dont think multiply = 1 is valid, the smallest is 2 so you need to use M=2 D=4

otherwise what you did looks correct, we do it same way and it works (but we use valid M and D params of course)

Antti

Reply to
Antti Lukats

im.de napisa³(a):

Is that any special needs to use DCM? If I were You I would use just flip-flop. It'll be faster for lock - instant, and 50%-50% low-high.

If you must use DCM, make it like Antti Lukats wrote.

Best regards

Jerzy Gbur

Reply to
Jerzy Gbur

Or you can use just DLL part of DCM that will give you a fixed divided output clock @ 1/2 ofinput clock.

-James

Reply to
dexue

I think that the problem is in multiply settings, as the minimum value of M is 2. But did not you get a warning in the synthesis about this?

Vladislav

Reply to
Vladislav Muravin

All good advice:

Use the CLKDV output with DV=2 (divide by 2)

That is using the DLL part of the DCM, and it will have less jitter than using the CLKFX output with M=2, D=4 (M=1 is not a valid choice).

If you use the CLKFX to do this, be aware that the min frequency now applies to the output (CLKFX must be greater than 24 MHz, or whatever the min freq spec is for the part).

Austin

Reply to
austin

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