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

T&E,

Have you tried swapping the 8255 from the working circuit with the 8255 in the non-working circuit?  The 8255 came in various timing flavors as well as NMOS and CMOS versions.  Years ago I had a circuit that would only work with the CMOS version.  Rather than spend time figuring it out, I simply bought CMOS chips and everything worked fine.  Are the 8255 chips you're using identical in every way?  

Thanks,
PeterM

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