• 0
frank2020

a7 external clock

Question

Would like to use an external 100 MHz clock for the A7. Assume that we would use a pair of Artix MRCC pins, e.g. PIO36/PIO40 or PIO18/PIO19. How do we handle existing on-board clocks?

Share this post


Link to post
Share on other sites

8 answers to this question

Recommended Posts

  • 0

Jon,

Thanks for your reply.

We're using the Cmod A7. Checked the board and see that the ASEM1-100.000MHZ-LC-T is not populated. We'd like to clock the A7 with 100MHz LVCMOS; but, still be able to talk to it via USB. What would be the best way to setup clock domains?

Share this post


Link to post
Share on other sites
  • 0

It looks like external clock is not recommended for Cmod A7. 

Edited by Alex

Share this post


Link to post
Share on other sites
  • 0

@frank2020,

I may not be understanding your question but since you reference the unpopulated ASEM1-100.000MHZ-LC-T I'm assuming that you don't need your 100 MHz clock to be synchronous with an external component. Is there a reason why you don't want to use an MMCM to create a derived clock from the USB 12 MHz clock input? That's what I did in my CmodA735T demo. You can find it in the project vault. If you want to feed a clock into your design through one of the IO pins PIO36 on the Cmod A7-35T goes to a clock capable pin. Any MRCC, SRCC type _P IO pin will do.

CORRECTION!!! The following comment should be ignored...

The schematics aren't complete but it looks like you don't want to try soldering a ASEM1-100.000MHZ-LC-T component onto your board as its output is tied to the USB 12 MHz clock output through a 50 ohm resistor.

 

Edited by zygot

Share this post


Link to post
Share on other sites
  • 0

Hello zygot,

Thanks for your reply. Actually we do want to have the 100 MHz clock synchronous with an an external 100 MHz reference; don't want to derive a 100 MHz clock from the 12 MHz USB input. We do want to be able to talk to the Cmod A7 via USB also.

Regards,

frank2020

Share this post


Link to post
Share on other sites
  • 0
On 18/6/2017 at 3:50 AM, zygot said:

@frank2020,

"---The schematics aren't complete but it looks like you don't want to try soldering a ASEM1-100.000MHZ-LC-T component onto your board as its output is tied to the USB 12 MHz clock output through a 50 ohm resistor."

But I think is possible to remove the R80 resistor in order to decuple the USB_12MHZ clock line from the GCLK and then soldering the U4 to use a 100 MHz clock source, I'm wrong?

Thank

Best regards

Grinch

Edited by BYTEMAN

Share this post


Link to post
Share on other sites
  • 0
9 minutes ago, BYTEMAN said:

But I think is possible to remove the R80 resistor in order to decuple the USB_12MHZ clock line from the GCLK and then soldering the U4 to use a 100 MHz clock source, I'm wrong?

Yes, please check this post:

 

Share this post


Link to post
Share on other sites
  • 0

To all,

I got this one wrong. Unfortunately, I dealt with my faux pas on a different thread.... but @xc6lx45 is correct... as obviously others have found out. Unfortunately, when there are multiple threads talking about the same topic it's hard to backtrack and fix mistakes. Apologies to all.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now