i need some help ASAP !!! (DLL - Spartan-IIE)

Hi guys,

I must admit it's been a while since i have used Spartan2E; please help me with relatively simple issue, as i cannot find the answer to my question anywhere.

I am given a board, where I have XC2S400E device (FT256 package), and I have to make a design with what I have. I would like to use DLL. That is, I have an onboard oscillator of 25 MHz, which I would like to multiply by 2, and get 50 MHz (so fat, per datasheet DLL can accept a frequnecy starting from 25 MHz). FPGA device does not receive any external reset (do not ask why, I did not design the board).

Now, the question. I see that CLK2x output generates 25 MHz, not 50 MHz. Do I have to reset DLL??? It's just that before I ask to solder some wire for reset, I would like to be sure of that.

I saw in Virtex-II devices many times that there is no need for resetting DCMs, and the frequency they produce is just fine.

Thanks a lot in advance.


Reply to
Vladislav Muravin
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Vladislav -

Why not create a reset signal in the chip that holds the DCM reset after configuration? The SRL16 shift register starts up after device configuration in a known state. Have it shift out areset signalfor a16 cycles at the 25MHz as the reset to the DCM. You can also use this (with a bit more logic) to reset the rest of your design.

John Providenza

Reply to

you could refer to the XAPP174 on Xilinx website. It gives some codes and those codes could be used in you design immediately.

Reply to


Sorry to bother all, i have had a stupid problem && mismatch to this xapp

174. I did it in the way i am used to do with V2.

thanks a lot


Reply to
Vladislav Muravin

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