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Requesting Help identifying an Atari 800 RAM upgrade

Atari 800 Axlon RAM

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#1 JohnBuell OFFLINE  

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Posted Sat Nov 25, 2017 2:51 PM

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.

20171124_163903.jpg

 

OS Board

20171124_163931.jpg

20171124_163956.jpg

RAM from slot 1

20171124_164206.jpg

20171124_164225.jpg

 

RAM from slot 2, with physical switch

20171124_164258.jpg

20171124_164314.jpg



#2 sup8pdct OFFLINE  

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Posted Sat Nov 25, 2017 4:34 PM

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



#3 JohnBuell OFFLINE  

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Posted Sat Nov 25, 2017 6:56 PM

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.

#4 _The Doctor__ ONLINE  

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Posted Sat Nov 25, 2017 8:45 PM

make sure the last 16k module is actually a 16k module as the are not always whats on the label



#5 a8isa1 OFFLINE  

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Posted Sat Nov 25, 2017 9:49 PM

I've never seen one but could this be the Byrd 256K upgrade?

 

[EDIT]

Description here

 


Edited by a8isa1, Sat Nov 25, 2017 9:56 PM.


#6 _The Doctor__ ONLINE  

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Posted Sat Nov 25, 2017 10:11 PM

That's the upgrade, and my interest in if the last 16k was modified



#7 x=usr(1536) OFFLINE  

x=usr(1536)

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Posted Sun Nov 26, 2017 7:47 AM

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), Sun Nov 26, 2017 7:58 AM.


#8 1050 OFFLINE  

1050

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Posted Tue Nov 28, 2017 5:27 AM

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.

#9 ClausB OFFLINE  

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Posted Tue Nov 28, 2017 6:25 AM

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.

#10 1050 OFFLINE  

1050

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Posted Tue Nov 28, 2017 11:51 AM

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.atarimani...uments_3_8.html

http://atariage.com/...e/#entry3187242

Jerzy Sobola
http://www.dereatari...pl/schematy.htm

#11 ClausB OFFLINE  

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Posted Thu Nov 30, 2017 10:08 AM

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.

#12 a8isa1 OFFLINE  

a8isa1

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Posted Thu Nov 30, 2017 10:54 AM

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...



#13 ClausB OFFLINE  

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Posted Thu Nov 30, 2017 4:06 PM

I don't think Byrd got the refresh circuit right. So if you're building one from scratch, see this thread: http://atariage.com/...e/#entry3320548





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