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JohnBuell

Requesting Help identifying an Atari 800 RAM upgrade

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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.

post-10340-0-97416800-1511642461_thumb.jpg

 

OS Board

post-10340-0-79892600-1511642524_thumb.jpg

post-10340-0-53363300-1511642559_thumb.jpg

RAM from slot 1

post-10340-0-77463200-1511642591_thumb.jpg

post-10340-0-70986400-1511642655_thumb.jpg

 

RAM from slot 2, with physical switch

post-10340-0-21037100-1511642718_thumb.jpg

post-10340-0-67959200-1511642758_thumb.jpg

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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

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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.

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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 by x=usr(1536)

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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.

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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.

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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

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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.

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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...

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