Tim,

  I used an 8255 in every Z80 system I built, and when I moved from Z80 to the BASIC Stamp the reason I didn't consider using the 8255 because of the number of I/O lines required to do so.  I admire your determination though.  Just pains me to see all those I/O lines in use.

Well something I forgot about with the 8255 is that it is actually the 82C55-A where the C is CMOS which can be destroyed very easy with the slightest of static. I took it out of my breadboard last night and put it back in this morning and it is dead. At $9 it is a bit expensive to loose to only develop within 1 day usage. Anyway, I am going back to 74HC595's but the memories were there.

I did try to develop today with a couple of 74154 (4-16 line decoder) and a 74LS193 (up-down 4 bit binary counter) to find a way to use this combination with my LED moving display sign project (because it can change directions). I still can't find a way to cascade 2 74154 IC's unless I use an extra address line (5 not 4) but we'll see. I don't believe these are as static sensitive as CMOS chips like the 82C55-A and are going strong so far.

The parallel 82C55-A has been put to rest and I'm moving forward with serial chips like the 74HC595s.

Timothy Gilmore

I decided to open up the case again on the 8255 issue of this not working in my circuit. I have tried 5 more 8255's and none of them work. Is it possible that all of them are bad?

It's driving me a bit crazy that when I take one right out of the packaging and plug it into my Professional Development Board (all wired to the schematic previously attached - also used a BS2 and BS2px and neither provided a working 8255).

Can anyone verify or at least look over my code and let me know if I am doing anything wrong. This was working a year ago that is why it is so crazy.

I just ordered 9 more 8255A's on Ebay (using a different source than Jameco) and also a 1979 book on Ebay entitled "Microcomputer Interfacing with the 8255 PPI chip" so I'm hoping this will help.  
 

Comments?

Thanks.

They are working!!!

A friend of mine in the ZX81 community helped me with the initialization routines and timing. I was close but in some ways - off the mark. I have updated all of the programs and drawings and they are significantly different.

I plan on implementing this into a ZX81 design.

The programs now allow for up to 4 8255's with 1 BS2 or BS2px. This means you can have up to 96 I/O lines with simple code changing. The additional lines P12-P15 are for Chip Selects for 4 8255's.

I still am not sure why it originally worked but it works CORRECTLY now with no guess work and plenty of commenting.

Thanks. 

Thanks Bill.

I really like working with the "old stuff". I just can't believe how hard it was to find info on how to use it other than the datasheet. We'll at least my work did not go in vain.

Thanks.

   I was actually going to dig out my Z80 source code for one of my old controllers last night, but I read the thread too late and T&E got his answer already.  The 8255 was my PIA of choice even for the Z80.  Although I will admit for things like a keyboard interface I preferred simpler solutions, such as a 74LS374/74LS244 combo.