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DCM in FPGA

Former Member over 9 years ago

Hi All,

i need to divide my CLK form 100Mhz to 200Hz. Can i do it with DCM?

what is minimum freq till DCM works optimium.

Thanks to All

Noman

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michaelkellett over 9 years ago +1

Why should you need a DCM to divide your clock by 500,000 - you can do this in the fabric easily. If you want to understand the DCM then I suggest you start by reading the manual - (ug382.pdf on Xilinx…

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johnbeetem over 9 years ago

I agree withmichaelkellett: just use the fabric. With 100 MHz, you probably want to do the division in two stages. Dividing 100 MHz to 200 Hz is a lot to squeeze into a 10 ns cycle, so I suggest having a prescaler followed by the regular counter, as I do in Experiment 2 of this 'blog: First Experiments with the ValentF(x) LOGI-Pi.

You can also use a DCM as a prescaler, which lets you distribute a lower-frequency clock which may save power. OTOH, the DCM may end up using more power.

I sometimes use an advanced trick where I use a gated clock as a low-speed clock to save power. I do this in my Flavia project. if you're interested, see module FlaviaClk in FlaviaX6.v in Data files for FlaviaLP60 release 0.0q for LOGI-Pi.
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johnbeetem over 9 years ago

I agree withmichaelkellett: just use the fabric. With 100 MHz, you probably want to do the division in two stages. Dividing 100 MHz to 200 Hz is a lot to squeeze into a 10 ns cycle, so I suggest having a prescaler followed by the regular counter, as I do in Experiment 2 of this 'blog: First Experiments with the ValentF(x) LOGI-Pi.

You can also use a DCM as a prescaler, which lets you distribute a lower-frequency clock which may save power. OTOH, the DCM may end up using more power.

I sometimes use an advanced trick where I use a gated clock as a low-speed clock to save power. I do this in my Flavia project. if you're interested, see module FlaviaClk in FlaviaX6.v in Data files for FlaviaLP60 release 0.0q for LOGI-Pi.
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