Questions about using DDR2 for Spartan3E

[Ansonng]

Using DDR2 for Spartan3E

I plan to use a Spartan3E on my design and I want to have a DDR2 also.

I read some document. SSTL18 class 2 is needed to interface DDR2. However, I found that Spartan3E only support SSTL18 class 1. Does it mean Spartan3E cannot support DDR2? What is the difference between class 1 and class 2?

Besides, even if the IO standard is supported, shoud I consider the clock frequency as well. What is the key consideration to use DDR2 in terms of Specifications? Thank you very much for your answers.

 

[banjo]

Using DDR2 for Spartan3E

I believe the difference is between the two classes are the class 1 drivers are weaker. They can supply less current on output pins and there output voltage levels are a little bit less when loaded.

If you are doing a Spartan3E to a direct DDR2 dram chip, I do not think it will be too much of an issue. However, if you are trying to drive a DDR2 module or a bus, it would concern me.

Why exactly do you want to add external memory? What speed do you have to run at? There are several other choices with like DDR1 or SDRAM or even static ram. It all depends on what you want to accomplish.

I would spend some time with the Xilinx App Notes, there are numerous ones dealing with these memory interfaces in all FPGA families back through the original Virtex chips.

It is sometimes a mistake to always assume that you need the latest and greatest. Often using a technology that is previous to the current one has many advantages. Lower cost and a solid foundations of other whom already worked out the bugs.

Xilinx has some IP cores that can simplify the memory interface. Again, the cores seems to work best on the slightly older technology because of the bugs have been hammered out by previous users.