Hi,
I'm working on a Virtex4 DDR2 interface based on the direct clocking design from MIG 1.6 (XAPP701). I'm clocking the DDR2 (Micron 1Gb) at
125MHz, so I would expect to see only one edge of DQS during calibration using the IDELAY. However, from chipscope I see two edges only approx 900ps apart. I notice there are lots of IDELAY queries on here... can anyone explain what is going on? The design uses an IDELAYCTRL clocked at 200MHz from a DCM CLKFX with a 50MHz clkin.The result is intermittant read errors, I suspect since the calibrated data delay is totally wrong...
Many thanks,
Rob