Replacing PCMCIA SRAM card?

Hi,

I'm working with an old design that uses PCMCIA SRAM cards to store data.
Today these cards are very expensive so I wonder if I can replace the SRAM
card with a Flash card. I was thinking of using a Linear Flash card but I've
never used such a thing before. I don't know how different they are from
SRAM. SRAM card was simply a memory space in my microcontroller's view so
there was really no problem. I know that I can READ the linear flash card
the same way but I wonder how I can write to it. In my application, each
address location will only be written once (it's a DAC application), though
I don't know if this information will help or not. Is it possible to erase
the flash card and then to do a random write to address locations (bytes or
words) on it? What other options do I have besides PCMCIA linear flash? I
need minimal changes from SRAM card protocol as the development in this
project is basically freezed and these changes are just a maintenance not a
complete redesign. Any help and insights would be appreciated.

Regards
Arash

Arash Salarian <arash dot salarian at epfl dot ch> wrote:
> Hi,
> 
> I'm working with an old design that uses PCMCIA SRAM cards to store data.
> Today these cards are very expensive so I wonder if I can replace the SRAM
> card with a Flash card. I was thinking of using a Linear Flash card but I've
> never used such a thing before. I don't know how different they are from
> SRAM. SRAM card was simply a memory space in my microcontroller's view so
> there was really no problem. I know that I can READ the linear flash card
> the same way but I wonder how I can write to it. In my application, each
> address location will only be written once (it's a DAC application), though
> I don't know if this information will help or not. Is it possible to erase
> the flash card and then to do a random write to address locations (bytes or
> words) on it? What other options do I have besides PCMCIA linear flash? I
> need minimal changes from SRAM card protocol as the development in this
> project is basically freezed and these changes are just a maintenance not a
> complete redesign. Any help and insights would be appreciated.
> 

I'm afraid that the availability of linear flash might soon be as bad
as for SRAM. The major companies that used to make them seems to have
dropped PCMCIA memory cards completely and left it to smaller players.

The fact that you will only write once to each cell during normal
operation will make your life easier. Writing to flash requires a
certain algorithm. Generally the algorithm is similar but not
identical for all brands, and sometimes there are minor differences
between different versions from the same manufacturer. This means that 
if the card you've tested with disappears from the market you may have 
to modify your software to use a different card (or buy enough of the
old model to last the lifetime of your product).

In short, it is possible to erase the Flash card, generally you erase
it sector by sector. You can then write byte by byte using the
appropriate command sequence (algorithm), but not exactly "random write"

We used AMD and Fujitsu, but they don't seem to have any data sheets
on their web sites any longer, so I can't point out any refrerences
on how the algorithms work.

It seems like it should work in your application, but it will take a
bit of work and it's probably not a good long term solution. But then
perhaps you don't need a long term solution...


/Henrik

-- 

>
> It seems like it should work in your application, but it will take a
> bit of work and it's probably not a good long term solution. But then
> perhaps you don't need a long term solution...
>

Thanks for your answer. It seems there is no way to keep compatibility with
both SRAM and linear Flash cards with just simple measures (not to rewrite
the microcontrollers' program). The problem is over the years, lots of
clients have bought our device and it is too much effort to upgrad all the
firmwares of all our old devices.
You know, with such crazy prices for SRAM cards, I think if I use a FPGA
chip and a normal SD or CF module and put them inside the box of a SRAM
card, I can save much more time and money! Then again, who knows, maybe I
can do it...