Atari 600XL SRAM

[ClausB]

Thanks. Yes I wrote that demo in the day for an Axlon 128K equipped 800.

http://atariage.com/forums/topic/126109-page-flipping-animations/?hl=%2Brecognizer&do=findComment&comment=1524729

[Ralphy Rocket]

There it is! :-)

 

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[ClausB]

Another simplification to the circuit: Don't bend up U6 pins 9 thru 11 and connect SRAM A16 to U6 pin 1.

 

For posterity, here is the simplified mod:

 

Bend up pins 1 thru 4 and 15 of an LS158 and plug it into socket U5. Bend up pins 1 thru 7 of the other LS158 and plug it into socket U6. Then connect the bent up pins as follows:

U5-1 to A15

U5-2 to A14

U5-3 to Gnd

U5-4 to U6-1

U5-15 to PB4

U6-1 to SRAM A16

U6-2 to PB3

U6-3 to A14

U6-4 to SRAM A14

U6-5 to PB2

U6-6 to A15

U6-7 to SRAM A15

[gozar]

Now, what about upgrade a 400? :-)

[ClausB]

Done.

[gozar]

I was hopping for some static ram goodness. :-) Well, assuming it would be easier.

 

 

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[Jinks]

Here is a dumb question. What is the advantage doing a sram upgrade such as this than the already proven 64kb 600xl mod? Just wondering.

[+David_P]

SRAM is easier to interface than DRAM.

[Ralphy Rocket]

and easier to get....

 

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[Mercenary6502]

I was hopping for some static ram goodness. :-) Well, assuming it would be easier.

 

 

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I was actually thinking about doing a 400 next with SRAM. Might pick one up sometime soon. Plus perhaps make it XL compatible just for the challenge as far out as that might sound?

[Mercenary6502]

Well, here's the finished product:

 

An Atari 600XL that's XE compatible with 128k of RAM and includes REV C Basic, three built in 8k games (PacMan, Super Breakout, and Space Invaders), and USB for use with the Aspeqt software. By all means not the most extreme and impressive ever, but I'm still proud

 

 

A couple notes: The games are selected with two switches on the back of the unit and I made a small cut to the RF shield so it could be reused (switches were too high). So the computer should run as quiet as it did before as far as emissions go.

 

I may end up selling it after I'm done playing with it, but nothing is set in stone. Anyway I promise I'll stop nagging now, just though I would show the final pics

[Mercenary6502]

and easier to get....

 

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That and very cheap from the right sources. Along with those two reasons, I wanted to do something that others could do as an alternative when that old DRAM REALLY can't be found. Which I don't think is too far off from now.

[Joey Z]

 

I was actually thinking about doing a 400 next with SRAM. Might pick one up sometime soon. Plus perhaps make it XL compatible just for the challenge as far out as that might sound?

I've already done that with DRAM, to some extent. The atari 48K upgrade for the 400 had 64K of RAM, so I made a simple circuit to upgrade to XL compatible.

[Mercenary6502]

I've already done that with DRAM, to some extent. The atari 48K upgrade for the 400 had 64K of RAM, so I made a simple circuit to upgrade to XL compatible.

Nice. I briefly looked into it but doesn't the 400 switch it's RAM banks in 4k blocks instead of 16k? Isn't that the main XL compatibility issue even with 64k?

[Mercenary6502]

Looking at this, Maybe it was only with that 48k+16k upgrade from Mosaic that divided the extended 16k into 4 4k blocks.

[Joey Z]

Nice. I briefly looked into it but doesn't the 400 switch it's RAM banks in 4k blocks instead of 16k? Isn't that the main XL compatibility issue even with 64k?

I think you're thinking of Axlon memory upgrades. My memory upgrade took a card that was 64K, but only 48K accessible, and I made the remaining 16K XL style banking.

see here: http://atariage.com/forums/topic/206906-64k-400-upgrade/?hl=atari+400+64k

the links to the images are dead now, unfortunately, but I think it doesn't matter all that much since I think my machine was the only one to ever receive this upgrade, due to complexity of building and lack of interest.

Regardless, the principal is similar for SRAM, as far as the chip select logic goes. You'll need a way to grab all the address lines for the SRAM, you'll need a way to disable the cartridge region RAM when a cart is plugged in (wires to RD4/RD5 on the cart port), and some circuitry to detect when you're doing an OSROM region access, and either enable the RAM or the ROM depending on the state of PORTB bits. You'd also need to replace the OS with an XL OS. Self test support is ideal, as most XL ROMs don't like not having it (which is why I was forced to use the 1200XL OS on my upgrade, since I had not implemented self test).

[Mercenary6502]

I think you're thinking of Axlon memory upgrades. My memory upgrade took a card that was 64K, but only 48K accessible, and I made the remaining 16K XL style banking.

see here: http://atariage.com/forums/topic/206906-64k-400-upgrade/?hl=atari+400+64k

the links to the images are dead now, unfortunately, but I think it doesn't matter all that much since I think my machine was the only one to ever receive this upgrade, due to complexity of building and lack of interest.

Regardless, the principal is similar for SRAM, as far as the chip select logic goes. You'll need a way to grab all the address lines for the SRAM, you'll need a way to disable the cartridge region RAM when a cart is plugged in (wires to RD4/RD5 on the cart port), and some circuitry to detect when you're doing an OSROM region access, and either enable the RAM or the ROM depending on the state of PORTB bits. You'd also need to replace the OS with an XL OS. Self test support is ideal, as most XL ROMs don't like not having it (which is why I was forced to use the 1200XL OS on my upgrade, since I had not implemented self test).

Man yeah, that is a lot of work. I was also wondering about the OS ROM.

 

Because of all the work involved, I think this computer needs some professional module boards that can be dropped in to save some work. But without enough interest, it wouldn't be worth the trouble and cost of designing them.

[Joey Z]

Man yeah, that is a lot of work. I was also wondering about the OS ROM.

 

Because of all the work involved, I think this computer needs some professional module boards that can be dropped in to save some work. But without enough interest, it wouldn't be worth the trouble and cost of designing them.

provided you made it work in the 800 as well, I think there would most certainly be interest in them. I definitely agree that an as drop in as possible memory board would be the best approach here.

[Mercenary6502]

provided you made it work in the 800 as well, I think there would most certainly be interest in them. I definitely agree that an as drop in as possible memory board would be the best approach here.

I actually have an 800. Don't pull it out much, but it's there. So if I decided to go down that road, I could work with both machines assuming I would have picked up a 400 at that time.

Edited October 13, 2015 by programmer6502

[ClausB]

I think that, for a 400 or 800, Axlon compatibility is the way to go. XL compatibility is full of problems, including what do do about joysticks 3 and 4. Look how far Incognito went to solve those.

 

It wouldn't be too hard to do an Axlon-style SRAM upgrade. If you want to build it, I'll provide a design

[+Larry]

SRAM is easier to interface than DRAM.

 

I must be missing something... The above mod is easier than the Neff 64K? (BTW, I understand that this has more mods in it, but still...)

 

 

@ Programmer6502:

On the finished picture, what is right above the PBI that has a bundle of wires going to it? And on the back view of the case, there appears to be a hole cut in the case at the same location. Is that an IC glued on the inside of the case, and part of this mod?

 

-Larry

[+Larry]

SRAM is easier to interface than DRAM.

 

I must be missing something... The above mod is easier than the Neff 64K? (BTW, I understand that this has more mods in it, but still...)

 

 

@ Programmer6502:

On the finished picture, what is right above the PBI that has a bundle of wires going to it? And on the back view of the case, there appears to be a hole cut in the case at the same location. Is that an IC glued on the inside of the case, and part of this mod?

 

-Larry

[+Larry]

SRAM is easier to interface than DRAM.

 

I must be missing something... The above mod is easier than the Neff 64K? (BTW, I understand that this has more mods in it, but still...)

 

Edit: An afterthought -- did anyone ever take the Neff 64K on up to 256K using 256X4 drams? I don't recall it, but seems feasible.

 

 

@ Programmer6502:

On the finished picture, what is right above the PBI that has a bundle of wires going to it? And on the back view of the case, there appears to be a hole cut in the case at the same location. Is that an IC glued on the inside of the case, and part of this mod?

 

-Larry

[ClausB]

IIRC, 256Kx4 DRAMs need a 9-bit refresh address and the 600XL provides 8. So that adds at least two more chips to the mod.

[+Larry]

Replace the Antic and MMU?

 

-Larry