Mid-capacity RAM with serial connection to MCU?

I have also been looking for this type of thing, but I cant find anything. The only option I see is to use another small CPU and progrsam it to act like a serial RAM chip.

-howy

You might consider FRAM from Ramtron: 4k, 16k, 64k or 256k serial devices available. Access speeds are good, reasonable range of voltages supported (2V7 ... 5V5) depending on part.

Andrew

I've had good results with the 32kx8 SPI serial FRAM chips from RamTron. You get the added bonus that the data in the chip is non-volatile. The SPI versions will run as fast as the SPI bus on the MSP-430. Like other serial RAMs that require sending an address and command before reading and writing data, you get much better performance reading and writing blocks as opposed to random bytes.

Mark Borgerson

Thanks very much for the pointers - I just looked at the FRAM stuff, interesting certainly (wasn't aware of that technology)..... My application involves communications (continuous buffering of packets, etc.), so non-volatility is unnecessary, and counter-driven block-optimized addressing is actually a big plus, but I'm not at all comfortable with devices having finite write cycle lifetime. I guess I'm just suprised that regular static RAM for SPI type buses isn't a big enough market to drive product development. Dave.

I would rather thik of changing the MCU to the one that has the proper amount of RAM on board.

There is MSP430F1611 with 10KB of RAM, F1610 with 5 KB, and there are several cheap ARM chips with 8 or 16 KB RAM (or even more than that) - Atmel, Philips.

It's generally not a good idea to connect RAM to the chip that was designed to operate standalone.

A couple of points to take a look at - I believe the wear out mode for FRAM is to become the equivalent of a volatile SRAM (as you were initially looking for) - the newer and usually larger devices claim and unlimited write cycle lifetime.

Robert

Some years ago there was a Dallas part DS1280 converting a byte-wide memory to 3-wire serial (up to 512KBytes). No idea, if it is still available.

Regards Klaus

Or you could use a small CPLD to make a simple parallel SRAM to SPI bridge. I am starting up on similar project using FPGA to interface parallel SDRAM to SPI. Micro would use SPI with defined addressing scheme to read and write SDRAM.