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BYTEMAN

Cmod A7-35T clock on board question

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Dear All,

I bought this board (I'm waiting to receive it) meantime I'm looking the electrical schematic and I've noticed about the clock frequency that IC4 (sheet 3/7 Rev B.1) should be a 100 MHz clock, also I can see a USB_12MHZ line that came into the GCLK line through a resistor R80, I kindly ask you if U4 is the predefinited source of clock of the FPGA and then R80 is not mounted into the board because I need to setup a design able to operate with a 50 MHz clock and if the supplied clock generator supplied with the board is 100 MHz I'm very happy.

Could you please let me know more about this point?

Thanks!

Best regards

Grinch

clock-detail.jpg

Edited by BYTEMAN

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Hi,

the default clock is 12 MHz, shared with USB. This is the low-cost / low-power variant (~USD 1 and 5 mA, to give some numbers)

Alternatively, de-solder R80 and put an oscillator (e.g. 100 MHz) into the free slot as IC4. This way you can pick a clock frequency for the application, and maybe get better stability / jitter.
There is at least one post where this procedure was done on a number of boards. The 12 MHz clock will work just fine in most cases.

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I post this also here, even though the audience is probably the same.

Yes, please check this thread:

Just to be very clear on the issue: Unless you understand the capabilities of the built-in MMCM / PLL functionality please do not mess with the board. The FPGA can generate just about any clock you like, internally from the 12 MHz reference. In particular, you can run FPGA logic at much higher clock speeds without need for additional hardware. Those who understand they have "unusual" requirements (for a general-purpose board), never mind...

 

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