Need lots of RAM capacity, how?

[patroclus]

I need to handle 16 Mbits (4 Mb) data using RAM, as Flash ROM is too slow to write and would take several minutes in best case.

The 2 options I see are :
* SRAM : Very easy to write and read, and VERY fast.
The problem with is is obvious.. there are no SRAM IC in the market that really match my needs. It is hard to find a 4 Mbits SRAM IC, and even in that case, I would need 4 chips. Also it's quite expensive.

* DRAM : Gets rid of SRAM problems. DIMM memory for PCs can be used too, which are HUGE and quite cheap.
The problem is the DRAM controller.. I would have to build a DRAM refresh circuit and so (using CPLD for example).

As I have no experience in DRAM projects, do any of you have any idea of which could be the best choice ?? Any advice ??

Thank you

 

[StupidDum]

What is your application that require 4Mb of RAM??
Which processor you using?

 

[patroclus]

It is for data storing.
It is to make a development cartridge for a videogame console (Super Nintendo), so what I want is to write a certain program to RAM, then conecting it to the console so it just reads and runs the program.

 

[Roff]

What do you mean by "16 Mbits (4 Mb)"? How many bits wide is your data?

 

[patroclus]

8 bits bus data.

 

[John Sorensen]

so what I want is to write a certain program to RAM, then conecting it to the console so it just reads and runs the program.

Wouldn't you need something non-volatile, like FLASH? Why do you care how long it takes to write, if you're just going to use it to read? Are you going to program it in-place? What happens when you cycle power?

16 Mbits (4 Mb) data using RAM

16Mbits is 2Mbytes

j.

 

[patroclus]

Sorry, I meant to say 32 Mbits ( 4 Mb)

Wouldn't you need something non-volatile, like FLASH?

I've been using Flash until now, but for 4 MBits. The problem is that I do want to program it quite often, and it is important to be as fast as possible now.

Are you going to program it in-place?

Yes, this is the reason why waiting more than 15 minutes is unaceptable now. I need to load a program and run as soon as possible.

What happens when you cycle power?

You mean turn off power?? It does not matter if it erases when power is turned off. Every time I want to run a program I write to RAM, if this does not take long, of course.

Another problem of Flash ROM is that it is difficult to fin chips of 16 Mbit, even 8 Mbits.

The idea of DRAM is to use PC's DIMM or SIMM memory, which is compact. I don't know if there're big DRAM IC in DIP package or whatever.

 

[bmcculla]

My recommendation is to stick with SRAM. DRAM has a whole bunch of problems that just arn't worth dealing with for a one off project. Just buy a couple 256k x 8 and be done with it. You might need a CPLD to sort out the addressing but that should be easy. Avnet has a good selection of big, fast SRAMs (the SOJ package is fairly easy to solder). Their Parametric search is ok, though a bit slow and cumbersome.

 

[patroclus]

Yes, that's what I thought.
There's only one problem, just one :

- It will take a LOT of space. I need 32 Mbits, so I'd need 16 chips! or 8 chips if I manage to get 4Mbits SRAM...

 

[bmcculla]

Cypress seems to have a 2M x 8. If you call arround you can probably find someone who will sell you a couple. Avnet lists them but I didn't spend much time looking for quantity 1 purchasable parts.

 

[Oznog]

As I have no experience in DRAM projects, do any of you have any idea of which could be the best choice ?? Any advice ??

Thank you

You could always go with a flash disk. Those are pretty fast and plentiful, and removable (if that's useful to you).

Keep in mind if you're talking about a microcontroller that the controller itself has limited speed. The fastest is 10 mhz instruction clock. Even the fastest assembly doing something dumb like clearing to 0's would probably need around 10 clocks at least for a write, clock high/low, increment counter, and a conditional branch. Copying data would take far, far longer.

 

[patroclus]

2M x 8 could be just great, and much easier than building a DRAM memory controller...

I live in spain and can't get all parts here in my local store, do you know any good place to buy this kind of parts, better if in Europe??

About Flash, I've been using FlashROM and I need something faster now. thanks for the tip anyway.

 

[bmcculla]

Give Cypress Semi a call and ask them where you can buy their SRAM products.

 

[gurgalesci]

Wow, 16 mbits? Isn't that kinda small? Mine has 2566. Sad...