JohnBuell Posted November 25, 2017 Share Posted November 25, 2017 So I got my father's Atari 800 out again recently, and tried to start figuring out just what upgrades he had done to it, and how they might be useful. He told me at one point, and this was something like 30 years ago, that he was trying to get the 800 so that it would work like an XL (I had the 800 XL). The OS board has had work done on it, and the #2 memory card has a switch. Using SysInfo, it shows a 1920K (!) Axlon RAM bank. Searching AtariAge last night, I couldn't find a way to get into that bank for testing it, but I was able to use a couple of ATR files off of my SIO2SD to get it to successfully create a RAM disk. But I still have no idea what the actual capacity is. Here are some photos. All cards in the Atari 800 with the top off. OS Board RAM from slot 1 RAM from slot 2, with physical switch 2 Quote Link to comment Share on other sites More sharing options...
sup8pdct Posted November 25, 2017 Share Posted November 25, 2017 Total ram installed is 256 +16+16 = 288K. It is unusual for mods on the os board like that. Should also check the mother board for mods as well. Axalon ram switching is usually done at $CFFF. 0=main bank. James 1 Quote Link to comment Share on other sites More sharing options...
JohnBuell Posted November 26, 2017 Author Share Posted November 26, 2017 Thanks, James! I haven't had the entire case open in a very, very long time, but I know the original video cord for TV display has been cut off. That's the only thing I would vouch for right now. If I get time tomorrow, I will try to get the entire case opened up and photographed. Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted November 26, 2017 Share Posted November 26, 2017 make sure the last 16k module is actually a 16k module as the are not always whats on the label 1 Quote Link to comment Share on other sites More sharing options...
a8isa1 Posted November 26, 2017 Share Posted November 26, 2017 (edited) I've never seen one but could this be the Byrd 256K upgrade? [EDIT] Description here Edited November 26, 2017 by a8isa1 1 Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted November 26, 2017 Share Posted November 26, 2017 That's the upgrade, and my interest in if the last 16k was modified Quote Link to comment Share on other sites More sharing options...
+x=usr(1536) Posted November 26, 2017 Share Posted November 26, 2017 (edited) make sure the last 16k module is actually a 16k module as the are not always whats on the label Agreed; definitely check what's inside. And apologies if any of the below is at all vague or inaccurate, but it's been a long time since I had a modified 800. My 800 ran a similar set of modifications back in the day, but with a much lower total amount of RAM (128K) in a 2x32K plus 1x64K configuration. At least one of the memory cards appeared to be a standard 16K Atari RAM card, but if you pulled it out you lost 32K. The part number on the OS card at IC location A401 corresponds to the Rev. B NTSC OS, so that IC at least is probably stock. The switch on card #2 may be there to select between regular 16K operation and however much memory was installed on it beyond that. I seem to recall that there were some modifications that supported this, but don't remember specifics. Does anyone have the pinouts for the RAM and OS cards available? I've searched but can't find them, and they'd definitely help with trying to figure out what's going on here. What I'm seeing is ringing bells but my mind's not quite dredging up the info. Edited November 26, 2017 by x=usr(1536) Quote Link to comment Share on other sites More sharing options...
1050 Posted November 28, 2017 Share Posted November 28, 2017 I've never seen one but could this be the Byrd 256K upgrade?It's quite close but no cigar, sorry. I have one of those and it uses D7xx as the banking address instead of CFFF or more accurately 1Fxx which is mirrored to be CFxx as the Axlon does it. This means you need special ramdisk drivers to even see it and I've not run across any that I didn't have to make in my own house for it. So for 'in the wild' software to see this one, it would have to be using a standard Axlon banking address is my take away - just can't figure out how. This one is taking D4xx and D6xx signals as inputs to the dead bug on the back of the OS card to produce it's activation register with somehow. The Byrd mod also came thru that same hole and connected to the same card edge this one does. But there just is no software for the Byrd. One of the irritating things about the 800 is the card edge isn't found laid out as it exists. The schematics put the connections where ever it's handy for them to draw them with no consideration to the actual card edge order. We have skips in the alphabet that need to be looked up then correlated to an image of card edge. So no, I don't know of any such artwork that would be so intuitive to use here to know what card edge does what. Unless Claus comes along and saves us, all I've got at this point. Quote Link to comment Share on other sites More sharing options...
ClausB Posted November 28, 2017 Share Posted November 28, 2017 It does look like the Byrd mod but modified to select banks like an Axlon. The nand gates added to the OS board are wired to S6 and A12, so they decode Cxxx instead of D7xx. But none of that is like 800XL RAM, so I'll urge you like the others to look at the third RAM board. For schematics, search the forum for Jerzy Sobola's work. 1 Quote Link to comment Share on other sites More sharing options...
1050 Posted November 28, 2017 Share Posted November 28, 2017 Thanks, Claus. My bad in post #8, I have been misreading the 800XL schematic in the wrong manner all these years then and it's just a happy co-inkydink that pin 7 for that 138 is D7xx just as it is here. The Byrd has a single wire from Z401 pin 7 thru the hole to that card slot edge as pictured here. And that means I can convert mine to be a real Axlon following this example. I'll be doing just that someday then. Thanks for posting the excellent how to do it pictures John. Original schematic along with Sams Photofact http://www.atarimania.com/documents-atari-400-800-xl-xe-technical-documents_3_8.html http://atariage.com/forums/topic/235441-whats-up-with-jerzy-sobolas-site/?do=findComment&comment=3187242 Jerzy Sobola http://www.dereatari.republika.pl/schematy.htm 2 Quote Link to comment Share on other sites More sharing options...
ClausB Posted November 30, 2017 Share Posted November 30, 2017 To convert your Byrd to Axlon, add a 74LS138 to the OS board instead of the nand gates. Wire S6 and A12 to pins 4 and 5, A11 through A8 to pins 6, 3, 2, 1, and pin 7 to edge connector 20. That will decode addresses CFxx, more safe than the whole 4K block at Cxxx. 2 Quote Link to comment Share on other sites More sharing options...
a8isa1 Posted November 30, 2017 Share Posted November 30, 2017 To convert your Byrd to Axlon, add a 74LS138 to the OS board instead of the nand gates. Wire S6 and A12 to pins 4 and 5, A11 through A8 to pins 6, 3, 2, 1, and pin 7 to edge connector 20. That will decode addresses CFxx, more safe than the whole 4K block at Cxxx. Ooh! I have a spare 16K board, 256K DRAMs, Byrd's instructions, SDX on a flashcart, ClausB's additions, and I'm wearing sunglassess... Quote Link to comment Share on other sites More sharing options...
ClausB Posted November 30, 2017 Share Posted November 30, 2017 I don't think Byrd got the refresh circuit right. So if you're building one from scratch, see this thread: http://atariage.com/forums/topic/242691-atari-800-256kb-upgrade/?do=findComment&comment=3320548 1 Quote Link to comment Share on other sites More sharing options...
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