Max SODIMM freq on Cyclone III

Hi luisalba

It's not so much the SODIMM that determines the frequency, but a bunch of other factors.

When Altera specs a memory interface type, there are different speeds, depending upon the speed grade of the device. Also, the assumption is made that the FPGA is driving a single device located "close by".

With SODIMMs, or any type of DIMM, you are often driving multiple devices in parallel. This additional capacitance affects the driver's ability to ramp the voltage up and down. The socket also adds to this. The best thing to do is run an IBIS simulation to see how the signals look.

I have seen DDR2 DIMMs driven successfully, but performance varied greatly depending on whether the DIMMs were single or dual rank.

Back to your original question, I believe CycloneIII is rated at 200MHz for DDR2 and 167MHz for DDR / SDR at the fastest speed grade and drops down from there.

Best regards,

Stephen

Thanks Stephen:

so 200Mhz is the maximum allowed speed (supposing the board layout is ok). So the maximum data rate is 200 * 2 * 64 = 25.6Gbps (100% efficiency)

Yes, I think you have the maths correct. Not sure how far away from a 100% you will be, but at least you have goal to head for!

Stephen