Hello All,
Does anyone know what the real max DCM CLKIN speed of Spartan-3E stepping 0 is. In the datasheets it says 90 Mhz but in the errata is says 120 MHz. We have one design (with clock feedback from an external pin) where it fails at 100 MHz... Does the same speed limit apply to the CLKFB pin as well..
Thanks,
Finn
Finn,
The stepping 0 program should be very conservative. I doubt what you are seeing is related to the 120 MHz limitation on the step 0 parts. Have you checked the incoming duty cycle?
And yes, both CLKIN and CLKFB share the same specifications. So you also need to check the duty cycle of the CLKFB as well.
We spec from 45% to 55% for all operation.
Aust> Hello All,
Austin Lesea" wrote in a message news:dtklfu$ snipped-for-privacy@xco-news.xilinx.com...
Thank's Austin for the reply.
I guess the 90 MHz is just a conservative "to be on the safe side" official spec. We'll check the duty cycle of both the CLKIN and CLKFB signals if we can. From our local FAE, we were told that the CLKFB max. freq. is the same as for the CLK2X output - but I guess it depends on whether the DCM is configured to lock on a CLK1X or CLK2X signal.
We use it with the multichannel SDRAM controller at 100 MHz. and the DRAM works without the DCM deskewing - so it is related to the DCM.
Thank's again,
Finn
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