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manboy

Output a user-defined 1.8V 24MHz clock from zedboard to other device

Question

Hello all,

I would like to generate a user-defined clock (1.8V 24MHz) out from the board. (for other devices)

After I use a clock_wizard to generate a 24MHz clock and make external, which pin is suitable for assignment?

1) Choose Pmod JA1 (EPP pin = Y11), however, the pin is 3.3V in default. Should I buy a Pmod level-shiftier ?

2) Is there any other proper external IO recommended? 

 

Thanks.

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On 7/29/2020 at 4:22 AM, manboy said:

I would like to generate a user-defined clock (1.8V 24MHz) out from the board. (for other devices)

The Zedboard FMC connector Vadj supports 1.8V logic. One of the differential PMOD connectors might work though, as you've surmised, you'll need to add a level shifter to make the signal compatible with whatever you want to drive it into. I'd say offhand that a bigger problem is getting your clock to its destination as a usable clock source. This depends of course on the needs of the device that you are driving.

Be careful of dual voltage logic level translators. Read the datasheet very carefully.

You can by inexpensive USB clock generator evaluation boards from most clock module vendors. This might be a better strategy.

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Hi @manboy,

If you want to use a Pmod port you would need some sort of level shifter; it doesn't have to be the Pmod level shifter (Pmod LVLSHFT), but it would work for translating the voltage from 3.3V to 1.8V. Vivado will probably complain that about those IO pins suited for clocking, but I believe it should still work at 24 MHz. I would probably use one of the differential Pmod headers (JC or JD) as they do not have series resistors to hinder clocking speed.

Alternatively, there are some clock pins on the FMC header (which will also support 1.8V via the VADJ jumper).

Let me know if you have any questions about this. Edit: Though it looks like zygot responded a few minutes before I did with very similar information.

Thanks,
JColvin

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