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eric_holtzclaw

CMOD A7-357 (DAB7A8D)

Question

I have an A7-35T.  The clock chip provided outputs 12 MHz.  I need a raw clock input of 32 MHz.  If I change out the clock chip on the board, will this cause the USB interface to quit working.

If so, will any of the PIO pins be acceptable for a clock input to the MMCM?

Thanks,

>>Eric

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@eric_holtzclaw,

If you need to use an external clock as part of an interface there are pins that are appropriate. Unfortunately, the current version of the schematic for the CMOD-A7 doesn't show the pin names for all of the IO banks connected to PIOxx pins. Any _MRCC or _SRCC pins will work. Absent a customer friendly schematic you can find pin names for all Xilinx devices in UG475.

According to an older version of the CMOD-A7 schematic module pins PIO36, PIO46, PIO43, PIO37, PIO18, and PIO19 are on MRCC type pins.

 

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Posted (edited)

Hi @zygot,

So I can ensure the correct schematics are available, which current schematic are you referring to that doesn't have these details? The current version that I am aware of (Rev B on it's Resource Center) shows all of these details on the 3rd page. Or am I misinterpreting what you are saying?

@eric_holtzclaw, to confirm, yes changing out the clock chip will cause the USB interface to break. There is a location where you can provide an external oscillator on IC4 (intended to be 100 MHz), though you would need to remove R80 so that it and the USB clock aren't interfering. Otherwise you can always using the clocking wizard to create a PLL to create your 32 MHz signal if you don't strictly need an external source.

Thanks,
JColvin

Edited by JColvin
added comment on clockin

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>> Otherwise you can always using the clocking wizard to create a PLL to create your 32 MHz signal if you don't strictly need an external source

was just about to suggest that... check the clocking wizard (use MMCM "primitive", not "PLL" for a 12 MHz input clock). Reading between the lines of your question, there is a good chance this will save you a lot of work with a few mouse clicks.

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@JColvin

So... I looked at both schematics again and was surprised to see that the same Rev B.1 schematic displays differently on Win7 using Foxit Reader than it does in Centos using the native Gnome poppler application. If I drag the cursor over the empty blocks for IO Banks 34, 35 and 16 while holding down the left mouse button on Centos the hidden text appears in a blue background. 

Thanks  (really!) for forcing me figure this out. I guess that PDF files aren't all things to all people.

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@zygot no problem, I'm glad I could help out.

For others reference (just in case there are other situations where the pdf displays differently than the two situations mentioned on this thread), this is what I see on page 3 of the schematic in my Firefox browser on my Windows 10 machine:

Thanks,
JColvin

Cmod A7 pg 3.png

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