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Cmod A7 Clocking


Go to solution Solved by jpeyron,

Question

The schematic diagram for the Cmod A7 shows a clock with part number ASEM1-100.000MHZ-LC-T, which is a 100MHz clock. However when I look at the actual clock component it says it's 12MHz chip, which I confirmed by scoping the output. Is there any way to get a 100MHz clock signal out of this board?

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@etownsend,

Why not use a PLL to multiply the 12.5MHz clock up to 100MHz?  You could use a clocking wizard for that purpose, or ... you could just instantiate a PLL component in your code.  If you go the latter route, you'll need to multiply 12.5MHz by something to get it between 800MHz and 1600MHz.  96 might be a good example.  You can then divide that clock down (all within the same PLL) by 12 to get a 100MHz clock.

Dan

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13 hours ago, sLowe said:

@etownsend

Another thing to note is that the part is a no load so if you want to add the IC you have the option to put it on yourself. Although [email protected] has a more practical approach using a PLL to achieve 100MHz. I personally use the Xillinx Clocking Wizard. Although it's not as fun as [email protected]'s way. :)

@sLowe, can you elaborate a little more on this? I don't think I understand what you're saying.

Edited by etownsend
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  • Solution

Hi @etownsend,

There is the option of adding a 100 MHz oscillator to the Cmod A7.  Here is a forum thread that discusses this option. The oscillator would be added to IC4. You can see this in the schematic here on the bottom of page 3.  This is a more complicated processes and requires removing R80 along with adding the oscillator to IC4. I would not suggest this option.  The other two suggestions @sLowe referred to are different ways to generate a 100 MHz clock one using the Xilinx Clocking wizard here(my suggestion as well). The other is referring to @[email protected] suggestion of using a PLL(phase-locked loop) to generate a 100 MHz clock. Here is another forum thread that discusses generating a different clock using MMCM dynamic clocking(a much more complicated way).

cheers,

Jon 

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