Hi,I'm actually doing schematics using the cyclone Iv gx evaluation board. I placed the same DDR2( Mircon MT47H16M16) but I wonder why there are only 40 caps (10x4 CN caps) when micron says to put caps on every signals ? Are theses caps only needed for DQ DQS and DM ?
Ok, fine.However, if these caps are required but not necessary, for which signals are they required for, to the extent there are only 40 caps but 61 ddr2a signals ?
These caps are placed to keep Vref plane as much clean as possible. You should add a cap near every termination resistor, but since You're probably using resistor networks (at least I did), then place at least one cap per resistor network. The common approach is to place 3 caps near one resistor network with values: 100nF, 10nF, 1nF.