If you can't find a serial RAM chip to do the job and you have
sufficient board space you might like to try binary counters such as
a CMOS 4040 for the address decoder. These will work fine if you do
not need random access. Just 2 control pins, clock and reset.
Use 2 chips for 256K. I've used this method to get 12 bit data stored
into Battery backed RAM at 10K samples/sec.

Tony.


Just when I thought I knew it all,
I learned that I didn't.