1
\$\begingroup\$

A while ago I asked this question about using a ram chip for generating VGA signal from an fpga. After reading the replies I realized there were considerable practical difficulties with doing that, and that my knowledge as a hobbyist was insufficient to make this work.

I now have a papilio fpga board and although I've for now abandoned my previous project for now I would like to interface this to an external static ram as a learning exercise.

So I was thinking of getting a static memory chip something like this one and making a small breakout board pcb for it (probably using seeed studio or similar to get it made), bringing out the pins to a female header row. I can then connect to my papilio using simple wires.

Now, assuming my soldering is up to actually making such a board, is there any reason why such a board wouldn't work? I realise that having 30 or so wires connecting the two boards probably limits the speed I'd be able to use the memory at, but was wondering if it would work at all and if so what access speed I'd likely be able to get working?

The purpose of this is mostly because I want to try it even if there are better solutions I could just buy... and to give me the hardware I need to understand making memory access controller in verilog. I don't expect this to be fast enough to generate video signals from but wondered what kind of speed I might expect to work with such an arrangement?

\$\endgroup\$
  • \$\begingroup\$ Maybe I need to be more specific... If I have a ram chip connected to an fpga by plug in leads, 18 address wires, 8 data wires and 2 control wires, what is a reasonal frequency I could expect it to work at... 100kz? 1MHz, 10Mhz, 50Mhz? Just looking for what is worth trying really. \$\endgroup\$ – John Burton Jan 24 '12 at 11:36
  • 1
    \$\begingroup\$ If you are making a breakout board for it you might as well go ahead and make it a wing for the Papilio expansion ports. Be relatively careful in your routing and you should be able to get 10-50MHz. \$\endgroup\$ – davidd Mar 8 '12 at 23:45
1
\$\begingroup\$

The speed of your communication depends on many different items such as:

  • The speed of your SRAM module
  • The type of interface you are using
  • The routing of the board

For the first one, you can get the info from the datasheet of your IC, many SRAMs have acess between 8ns to 120ns, so find that information and if the device is not very fast, then you can probably ignore the other 2 items on that list.

The SRAM you mentioned in your question has a access time of 12ns, which means the maximum "theoretic" access you can have is around 80MHz. Since you ar ebuilding your own breakout board, it is hard to say how fast you can acces this SRAM, my personal guess is 10MHz is safe, 20MHz if you have a very clean board. Anything more than that is going to be pretty difficult, unless you make a very good PCB.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.