Use port or xdata method to bank is wast many roms..each bank must have the common area...how can i design a sch use gal to bank only one common area to save roms???
Can you try and explain your problem more clearly? I cannot understand your question.
I believe that you will find it less expensive to dedicate the first part of each bank to the common area. It's very hard to find a small EPROM. The EPROMs most available and least expensive are 128 Kbyte or 256 Kbyte. But to answer your question. Assume that you have 3 each 64K EPROMs. Also, assume that you have a 32Kbyte common area in the first EPROM. Now program your GAL and Port1 select to offset the first 32K of each EPROM. Your design will appear to be addressing five banks of 64K but actually the first 32K of each bank resides in the low 32K of bank 0. I believe that you will find the GAL and bank mux hardware will cost more than the larger EPROM.