Peter,

Early in this thread you 'll find Erik questioning the use of the 8255's and it's power consumption is just one of those characteristics that back up his query and supports your suggestion for using the octal latches and buffers.

How ever, for one of a kind "project", building from the junk box isn't "wrong" per se.

On the use of PSEN i would continue to maintain that "in general" any data map decode that co-exists with external memory devices should use PSEN to qualify the decode. Especially where the device designer is not the coder.

regards,
p