64K Atari 800

[ClausB]

Back in the day, I went nuts with RAM upgrades. First I had an Axlon "RAM-Cram" (yes, really) 32K board put into my 400. They gave me the old 8K board back, and I wondered what to do with it. After gaining some electronics experience, I decided to "cram" 16K more in there, so that my 400 would be as good as any 800 out there (almost).

 

So I sawed the 8K board in half lengthwise, soldered the top half to the 32K board with ribbon cable and added some gates and 8 more 4116s (24 in all). The motherboard got 4 wires soldered between the cart slot and RAM slot for proper selection and deselection. I wrapped the RAM sandwich with electrical tape and jammed it into the tiny case. And the damn thing worked. I think that gave me the confidence (or foolhardiness) to do all the upgrades that followed.

 

When the 4164 DRAMs became affordable, I redid the 48K 400 and published an article about it in the September, 1982, MACE newsletter.

 

Then I got an 800 and modified its 16K board to 48K with 4164s, as shown in the attachment. It plugged into slot 1 and needed a loopback card (or a 16K board) in slot 2 for all the select signals. Guess what I used for the loopback? Yup, the bottom half of that old 8K board (I never throw anything away).

 

To be continued...

[FastRobPlus]

A cliffhanger! I'm betting this ends with a dimensional rift being opened.

[+warerat]

Back in the day, I went nuts with RAM upgrades. First I had an Axlon "RAM-Cram" (yes, really) 32K board put into my 400. They gave me the old 8K board back, and I wondered what to do with it. After gaining some electronics experience, I decided to "cram" 16K more in there, so that my 400 would be as good as any 800 out there (almost).

 

So I sawed the 8K board in half lengthwise, soldered the top half to the 32K board with ribbon cable and added some gates and 8 more 4116s (24 in all). The motherboard got 4 wires soldered between the cart slot and RAM slot for proper selection and deselection. I wrapped the RAM sandwich with electrical tape and jammed it into the tiny case. And the damn thing worked. I think that gave me the confidence (or foolhardiness) to do all the upgrades that followed.

 

When the 4164 DRAMs became affordable, I redid the 48K 400 and published an article about it in the September, 1982, MACE newsletter.

 

Then I got an 800 and modified its 16K board to 48K with 4164s, as shown in the attachment. It plugged into slot 1 and needed a loopback card (or a 16K board) in slot 2 for all the select signals. Guess what I used for the loopback? Yup, the bottom half of that old 8K board (I never throw anything away).

 

To be continued...

 

Hey, kind of like my slot 2 card where I removed the 4116s, muxes, buffer, and decoder. I dremeled a rectangular hole to squeeze a perf board with a 32K static for the main ram and a 512K static for the extended. Then I just kind of press-fitted it in there and closed the case hoping nothing would come apart...

[ClausB]

A cliffhanger! I'm betting this ends with a dimensional rift being opened.

OK, not very exciting now, but it sure was to a young computer geek with no life.

 

Maybe you're watching too much Torchwood?

Edited March 14, 2008 by ClausB

[ClausB]

Anyway...

 

So I had a 64K board with 48K usable. I hated to waste that extra 16K. I looked for a way to go beyond 48K without bank switching - maybe at least fill that 4K hole and get 52K. Well, slot 3 had an interesting signal called EXSEL which could disable the motherboard buffer between the ROMs and the CPU. So why not go all the way and switch in RAM in place of the ROM? That would give 62K RAM, leaving 2K for the I/O that makes an Atari an Atari. It would be just like an 800XL (sort of).

 

The attached schematic shows the circuit I made to do that. It plugged into RAM slot 3. It could enable RAM or ROM depending on the R/W line, so you could write-protect the upper RAM or even write to RAM while reading from ROM (handy for copying the OS to the underlying RAM). The circuit required a simple mod to the OS board's unused NAND gate, as well as a single motherboard jumper from the OS slot to RAM slot 3. It also needed a way to select the RAM in slot 1, forcing a minor wiring change to the RAM board. Software would write to addresses in page $D6 to control the switch. It was cool.

 

What ever happened to that 32K Axlon? After dismantling the sandwich, I upgraded it with 4164s to 128K and added some more chips to imitate an Axlon RAMdisk board for slot 2. That gave the 800 174K usable out of 192K of RAM.

 

To be continued...

Edited March 14, 2008 by ClausB

[FastRobPlus]

A cliffhanger! I'm betting this ends with a dimensional rift being opened.

OK, not very exiting now, but it sure was to a young computer geek with no life.

 

 

 

 

On the contrary - sawing a board in half would have been too much excitement for me back when these boards were worth serious money. Especially since I don't think dremels were around back then. I would not have had the guts to attempt this level of experimentation.

[ClausB]

Hey, kind of like my slot 2 card where I removed the 4116s, muxes, buffer, and decoder. I dremeled a rectangular hole to squeeze a perf board with a 32K static for the main ram and a 512K static for the extended. Then I just kind of press-fitted it in there and closed the case hoping nothing would come apart...

Cool! Which bank-switching scheme?

[ClausB]

Sorry, I got the sequence of events wrong. My notes were not dated but I deduce now that I did the 64K upgrade in 1983, after I had dissected a (rather nervous) club member's 600XL. So it did not predate the XLs. My apologies. I edited the original post to remove the claim.

 

BTW, I just noticed the similarity in pronunciation between the signal EXSEL and the model name XL. You think Atari intended that?

[Rybags]

Interesting.

 

So, which MACE? Melbourne, Montreal ... ?

[FastRobPlus]

BTW, I just noticed the similarity in pronunciation between the signal EXSEL and the model name XL. You think Atari intended that?

 

Interesting! A search on the web reveals that XL officially stands for "eXtended Line" which really sounds like a backronym made up by marketing.

Since engineers often give codenames to platform changes that are derived from a component that's changing, calling the new platform XL based on this would have been natural. I can even see marketing picking up on the name and keping it.

Edited March 14, 2008 by FastRobPlus

[ClausB]

Interesting.

 

So, which MACE? Melbourne, Montreal ... ?

Michigan Atari Computer Enthusiasts was a Detroit-area club with hundreds of members. I was in a smaller club in Lansing, called CHAOS, but some of us made the 1.5 hour drive to a few MACE meetings. They were spectacular - filled an auditorium with a big screen projection TV up front!

[ClausB]

Continued...

 

The idea of copying cartridge programs out of ROM and into the top of 48K RAM had been around for a while. Atari was countering this practice by adding code that randomly wrote into the ROM address space so that, if it were running in RAM, the program would destroy itself and crash the system. I thought I could use the write-protected RAM trick in the cartridge address space to thwart that, so I made the "SoftCart" circuit attached.

 

Plugged into the left cart slot, this 2-chip circuit enables RAM on power-up. You would then load the cart program into RAM, write to an address in page $D5 to write-protect the RAM, and restart the system. When it comes up, it thinks it has a ROM cart and runs it normally. How cool was that? No more swapping carts in and out, no more power down and power up cycles, just boot a disk that could hold 10 8K cartridge programs - games, BASIC, etc. It was great. A few months later a product appeared, called The Pill, I think, that did something similar. Opportunity lost.

 

That's as far as I took the 800 upgrades. Later, when I got an 800XL, the RAM upgrade bug bit me again. That story has been covered in the "RAM Upgrade Applications" thread.

 

Fin.

[miker]

Hey - put inside 1MB.

 

Why limits?

[+David_P]

Slightly OT:

 

The Montreal Atari Club was named at its first meeting "The Reunion of Atari Montreal People" or TRAMP. It was intended as a joke; at the second meeting the club was renamed the "Montreal Atari Club Atari de Montreal", or MACAM. Lots of memories there...

[+bf2k+]

On the contrary - sawing a board in half would have been too much excitement for me back when these boards were worth serious money. Especially since I don't think dremels were around back then. I would not have had the guts to attempt this level of experimentation.

 

Heheheh... I had a Dremel tool when I was 12... 40 years ago!

[ClausB]

Then I got an 800 and modified its 16K board to 48K with 4164s, as shown in the attachment. It plugged into slot 1 and needed a loopback card (or a 16K board) in slot 2 for all the select signals. Guess what I used for the loopback? Yup, the bottom half of that old 8K board (I never throw anything away).

[ClausB]

So I had a 64K board with 48K usable. I hated to waste that extra 16K. I looked for a way to go beyond 48K without bank switching - maybe at least fill that 4K hole and get 52K. Well, slot 3 had an interesting signal called EXSEL which could disable the motherboard buffer between the ROMs and the CPU. So why not go all the way and switch in RAM in place of the ROM? That would give 62K RAM, leaving 2K for the I/O that makes an Atari an Atari. It would be just like an 800XL (sort of).

 

The attached schematic shows the circuit I made to do that. It plugged into RAM slot 3. It could enable RAM or ROM depending on the R/W line, so you could write-protect the upper RAM or even write to RAM while reading from ROM (handy for copying the OS to the underlying RAM). The circuit required a simple mod to the OS board's unused NAND gate, as well as a single motherboard jumper from the OS slot to RAM slot 3. It also needed a way to select the RAM in slot 1, forcing a minor wiring change to the RAM board. Software would write to addresses in page $D6 to control the switch. It was cool.

 

What ever happened to that 32K Axlon? After dismantling the sandwich, I upgraded it with 4164s to 128K and added some more chips to imitate an Axlon RAMdisk board for slot 2. That gave the 800 174K usable out of 192K of RAM.

My memory (not my RAM) failed me when I posted this. Later on I opened my 400 and found the RAM Sandwich intact. Now I re-remember that I did the 48K 400 mod on a friend's machine in exchange for another RAM-CRAM which I later modded into a RAMdisk.

[ClausB]

The idea of copying cartridge programs out of ROM and into the top of 48K RAM had been around for a while. Atari was countering this practice by adding code that randomly wrote into the ROM address space so that, if it were running in RAM, the program would destroy itself and crash the system. I thought I could use the write-protected RAM trick in the cartridge address space to thwart that, so I made the "SoftCart" circuit attached.

 

Plugged into the left cart slot, this 2-chip circuit enables RAM on power-up. You would then load the cart program into RAM, write to an address in page $D5 to write-protect the RAM, and restart the system. When it comes up, it thinks it has a ROM cart and runs it normally. How cool was that? No more swapping carts in and out, no more power down and power up cycles, just boot a disk that could hold 10 8K cartridge programs - games, BASIC, etc. It was great.

[ClausB]

So I sawed the 8K board in half lengthwise, soldered the top half to the 32K board with ribbon cable and added some gates and 8 more 4116s (24 in all). The motherboard got 4 wires soldered between the cart slot and RAM slot for proper selection and deselection. I wrapped the RAM sandwich with electrical tape and jammed it into the tiny case. And the damn thing worked.

Actually, I covered the inside of the 400's shielding with electrical tape to prevent shorts. It was pretty tight. Axlon was kind enough to provide a spare IC position on the board so I could add the extra selection gates.

[Bryan]

So Claus, you designed the RAMBO? What was your relationship to ICD?

[ijor]

I thought I could use the write-protected RAM trick in the cartridge address space to thwart that, so I made the "SoftCart" circuit attached...It was great. A few months later a product appeared, called The Pill, I think, that did something similar. Opportunity lost.

 

Indeed! I understand that The Pill was quite a commercial success, and that it was CSS best seller product.

 

And what you implemented was actually the "Super Pill" (if I remember correctly the name). The PILL had a manual switch, only later (don't remember how much later) they implemented a "software" switch as you did.

[ClausB]

So Claus, you designed the RAMBO? What was your relationship to ICD?

I designed the original upgrade (see: http://www.atariage.com/forums/index.php?s...t&p=1481893 ) and put it into the public domain. ICD commercialized it but I had no relationship with them. I was pleased to see it on the market but I hated the name (thought the Rambo movies were stupid).

[labrat]

I've had a 400 for awhile that is pretty beat up and had 1 broken and 1 bent pin in the SIO port, so it has been on a shelf.

 

I recently opened it up and found that it appears to have been upgraded to 64K! The 64K chip seems to be made by Atari, but I can't find any info on it. There are some additional connections made between the cartridge and RAM sockets. I'll try to post pictures.

 

Anyone have any more info on this mod? Is it possible that the SIO port was intentionally modified, and not damaged as a result of carelessness as I initially assumed?

[ClausB]

I've had a 400 for awhile that is pretty beat up and had 1 broken and 1 bent pin in the SIO port, so it has been on a shelf.

 

I recently opened it up and found that it appears to have been upgraded to 64K! The 64K chip seems to be made by Atari, but I can't find any info on it. There are some additional connections made between the cartridge and RAM sockets. I'll try to post pictures.

 

Anyone have any more info on this mod? Is it possible that the SIO port was intentionally modified, and not damaged as a result of carelessness as I initially assumed?

It looks like one of these:

http://www.myatari.com/ebay/48k400.pdf

Thanks for posting the photos!

Edited March 3, 2009 by ClausB

[IndyJones1023]

Hey, Claus! I went to LCC for a year and spent some summers in East Lansing before that at my dad's. I recall a place called (I think) the Computer Castle. It was on Grand River or Saginaw. Do you recall that?