In SX Microcontrollers, SX/B Compiler and SX-Key Tool, mebikerider wrote:

I imagine you could get by with maybe 3 pins of control and 8 of data. Two control pins can address 4 selections which could latch the low 8 bits of address, latch the high 7 bits of address, send a WRITE command to RAM or send an OUTPUT ENABLE (READ) command to RAM. The third control line enables the selector to apply the address you've selected. 

If you wanted, you could use control 4 pins: two to directly control latching of two address latches and two to directly operate the RAM controls, and forget that HCT139 decoder.

From my experience with wire-wrapping a couple of Z80 microcomputer boards, if you're planning to build a 6502 system I'm sure that you'll know this sort of design inside and out by the time you're done.

David

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