In SX Microcontrollers, SX/B Compiler and SX-Key Tool, tdg8934 wrote:

Well....I moved the SX-28 to the PDB solderless breadboard (not the socket) and left the 8255 wired to the separate solderless breadboard and it worked.

Step 2. I moved the SX-28 back into it's socket on the PDB and left the 8255 wired to the separate solderless breadboard and it worked.

Step 3. I moved the 8255 onto the PDB (with the SX-28 in it's normal socket) and IT WORKED. 

HOW IS THIS POSSIBLE????

I originally had it like this and why should it all of a sudden work now?

Perhaps the SX-28 needed to be reseated back into it's socket?

Perhaps the wires were getting bent arround too much?

It still blows my mind on why it works correctly in the PDB now....

I don't know if I buy any of this but what I do know is that both the BS2 and SX-28 circuits work on the PDB with any 8255 chip. 

[b]Case closed.[/b] 

Wow this was a really hard one and very fustrating!!!!

Special thanks goes out to Metron9 who stuck by me and was able to go the extra mile to help!   Great Job!!!

My next step is to get a second 8255 (e.g. 48 outputs) to work with the SX-28 and BS2. This should be a piece of cake since I can have multiple CSx_8255 (chip select lines). I will post my findings probably in a new Thread. 

After this I will learn how to interface it to a ZX81 computer expansion port (which may or may not be of interest to this community). I have all of the right tools and equipment to make it happen. 

Thanks again Metron9!

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