xrbrevin Posted January 8, 2019 Share Posted January 8, 2019 check out this 800xl with a number of mods https://www.ebay.co.uk/itm/Atari-800xl-improved-motherboard/163475705431?hash=item260fe94e57:g:by0AAOSwA3xcEO96:rk:81:pf:0 it has a RAM mod, OS mod but can anyone identify the port mod above the SIO? it requires quite a few components. There is also something switchable on the PIA... Quote Link to comment Share on other sites More sharing options...
Rybags Posted January 8, 2019 Share Posted January 8, 2019 (edited) Looks like a parallel port - if you look for a datasheet for the 8255A chip prominent on the board you'll find it provides ports with switchable bits in similar fashion to the PIA. Other stuff going on - yeah it looks fairly extensive. Maybe they provide some sort of switching to redirect normal PIA I/O to the other port? Or it could be just to provide the addressability. Whether it's some known mod or totally custom/one-off, I don't know. I can't say I've heard of using that chip on the Atari, supposedly it's an Intel part so probably more commonly found in PCs/clones of the era. https://en.wikipedia.org/wiki/Intel_8255 Edited January 8, 2019 by Rybags 1 Quote Link to comment Share on other sites More sharing options...
flashjazzcat Posted January 8, 2019 Share Posted January 8, 2019 (edited) The big chip is an 8255, so my best guess is that this is a parallel port. EDIT: Gary beat me to it. I agree with the above anyway. Edited January 8, 2019 by flashjazzcat Quote Link to comment Share on other sites More sharing options...
+Nezgar Posted January 8, 2019 Share Posted January 8, 2019 And the switch beside the joystick port? 1 wire to C92, the other to the logic board for the RAM... Enable/Disable the 256K upgrade? Enable/Disable ANTIC banking? Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted January 8, 2019 Share Posted January 8, 2019 the OS mod, be dumped and mucking about could answered some questions about it all 2 Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted January 8, 2019 Author Share Posted January 8, 2019 i wondered if it was parallel port due to the DB connector but the XL already has a parallel port - would this mod be compatible with a different industry standard then? Quote Link to comment Share on other sites More sharing options...
flashjazzcat Posted January 8, 2019 Share Posted January 8, 2019 Parallel printer port: nothing to do with the XL parallel bus Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted January 9, 2019 Author Share Posted January 9, 2019 ah, that makes sense Quote Link to comment Share on other sites More sharing options...
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