Thanks for all the suggestions. I think I've found my "keep the hardware simple" solution by using an ordinary 2114 static ram. That way, just with 15 i/o lines (10 address, 4 data, 1 control), I can store 512 bytes by creating two small routines to read and write the data 4 bits at a time. Just one single 18 pin DIP! This is for accessing no more then two bytes at a time and only on specific events, not in a "main loop".