Using the Atari 400 48K board in the 800

[ClausB]

The Atari 48K board was meant for the 400 but with minor modification, an 800 can use it just as well. In this post I specified which pins to jumper on the 800 motherboard so that the board would work in Slot 1. Another poster wired and tested it. Since then another poster sent me an actual board and I built this schematic diagram (starting from Jerzy Sobola's 16K RAM schematic):

 

Notice that the board really contains 64K of RAM though not all is used. With this information I have designed a series of mods to the 48K board and the OS ROM board that should work without modifying the 800's motherboard or other internal board. So no disassembly of the case is required. Furthermore, the mods are reversible as no permanent damage is done to the boards besides soldering some wires and bending some pins. That should preserve the ever increasing value of these collectible machines.

 

Of the three mods, the first and simplest provides full 48K from Slot 1 alone. The second gives 52K, filling the 4K block at $C000 with RAM. The third mod allows RAM to take the place of the OS ROMs, as in the XL machines. Surprisingly, the board contains enough spare gates to implement the ROM/RAM switching.

 

I have not yet built and tested these mods, so anyone is welcome to try them and report on the results. I will post each mod here soon.

[+Faicuai]

(...)

 

Of the three mods, the first and simplest provides full 48K from Slot 1 alone. The second gives 52K, filling the 4K block at $C000 with RAM. The third mod allows RAM to take the place of the OS ROMs, as in the XL machines. Surprisingly, the board contains enough spare gates to implement the ROM/RAM switching.

 

I have not yet built and tested these mods, so anyone is welcome to try them and report on the results. I will post each mod here soon.

 

 

...NICE!

 

Seems like the foundation for finding the "whole grail". This is a highly-valuable project, and if someday can evolve into a final solution, well, that would be just wonderful.

 

Just make sure you leave the hooks for a future 1MB expansion as well... :)

 

F.

[+orpheuswaking]

Surely Jay Miner would turn over in his grave!

[sloopy]

(...)

 

Of the three mods, the first and simplest provides full 48K from Slot 1 alone. The second gives 52K, filling the 4K block at $C000 with RAM. The third mod allows RAM to take the place of the OS ROMs, as in the XL machines. Surprisingly, the board contains enough spare gates to implement the ROM/RAM switching.

 

I have not yet built and tested these mods, so anyone is welcome to try them and report on the results. I will post each mod here soon.

 

 

...NICE!

 

Seems like the foundation for finding the "whole grail". This is a highly-valuable project, and if someday can evolve into a final solution, well, that would be just wonderful.

 

Just make sure you leave the hooks for a future 1MB expansion as well... :)

 

F.

 

with an 800, it may be easier to just add another PIA...

 

 

sloopy.

[carmel_andrews]

Does that mean you can now play USG's 'Gauntlet' on an 800, although you'll have to change some of the code that refers to XL BS'g to working with old 800 BS'g (or any other XL game that uses XL BS'g)

[+orpheuswaking]

Sweet a twofer!

[ClausB]

Does that mean you can now play USG's 'Gauntlet' on an 800, although you'll have to change some of the code that refers to XL BS'g to working with old 800 BS'g (or any other XL game that uses XL BS'g)

Sorry, what's a BS'g?

 

The acid test will be whether most XL games will play on the modded 800.

[flashjazzcat]

Sorry, what's a BS'g?

Also - what's a "whole grail"?

[+orpheuswaking]

Sorry, what's a BS'g?

Also - what's a "whole grail"?

 

Dunno, but I think it's got hooks on it.

[ANTIQ]

It's what flower's made of.

[mimo]

its twice as good as half a grail

[+Faicuai]

Sorry, what's a BS'g?

Also - what's a "whole grail"?

 

 

Gee... I should have followed your advice... and document my stuff...

 

 

F.

[ClausB]

48K mod:

 

Remove the OS board from its case. Remove the 74LS09 chip from the socket at Z403. Solder a 6 inch length of wire to each of the pins 4, 5, and 9 of socket Z403 on the back side of the board. Reinsert the chip.

 

Take the Atari 48K board and remove the 74LS30 chip from the socket at U13. Solder a short wire between pins 2 and 3 of socket U13 on the back side of the board. Solder another short wire between pins 1 and 6 of socket U13. Now solder each of the 3 wires from the OS board to pins 4, 5, and 12 of socket U13, respectively. Reinsert the chip.

 

On the 48K board remove the 74LS32 chip from the socket at U15. Carefully bend up pins 3 and 11 so they stick straight out the sides of the chip. Reinsert the chip.

 

Wrap the 3 long wires over the top of the OS board. Plug the OS board into the 800's slot 0 (chip side toward the rear) and plug the 48K board into slot 1 (chip side toward the rear). Remove all other RAM boards from the 800. Close it up and test for 48K RAM.

 

Picture:

 

This mod is untested but I think it will work.

Edited July 29, 2011 by ClausB

[fibrewire]

ClausB: Are you up for a SRAM project using the Newell RAMROD board? I have a spare board that I can send to you in about a few weeks or so.

[iainjh]

Hi

 

Could you confirm the purpose of the third mod you mention? Does it improve / give 800xl compatibility for the 800 ?

 

I have an 800 and an xl, was watcing a few old threads for the past few years for a xl compatible 800 mod. Seemed like the others weren't ever going to happen, is this a way of gaining compatibility ? He says hoping

 

 

Cheers, nice work regardless!!!

[+warerat]

This may come off as a little strong, but please, quit busting my balls this upgrade. There are several people on this forum that I have modified OS boards to give 64K 800XL (and one even has a 576K version). Rather than doubt my claims, a simple polite PM would suffice.

 

I do have an active work life outside of this forum, and it requires me to travel. I'm sorry if my schedule and the way I've implemented the design (read: Facaui) does not meet your criteria. I would like nothing more than to mass produce it, but I cannot at this moment. Not saying that it will never happen, but the way I've implemented it to be an all-in-one solution and the constraints of the 800 is a little more involved than the skill set of most hobbyists.

 

Please correct me if I reading you wrong, but to modify an OS board (or Ramrod) to provide minimal 64K 800XL compatibility (with RAM under ROM) can be achieved easily and if it placates the community I will do a write up.

[fibrewire]

Warerat: Yep, this is exactly what I am looking for. RAMROD preferrably. Switches to switch between Atari 800/XL/XE

[+Faicuai]

I do have an active work life outside of this forum, and it requires me to travel. I'm sorry if my schedule and the way I've implemented the design (read: Facaui) does not meet your criteria.

 

 

 

 

...You have been excused eons ago. No need for you to feel compelled to seek or do what, in reality, you have not been asked for (at least not in this thread, though).

 

F.

[iainjh]

Warerat

 

Sorry if it read that way, I wasn't aware how that worked . Thanks v much for putting me straight. I didn't want to ask you in a pm as thought that was rude!

 

Best, Iain

[carmel_andrews]

BS'g= Bank Switching

 

Pretty obvious me thinks (given the context of the purpose of this upgrade)

[flashjazzcat]

BS'g= Bank Switching

 

Pretty obvious me thinks (given the context of the purpose of this upgrade)

Not to me it wasn't. Totally impenetrable, even after the third read. AFAIK, BS usually means "bulls**t". Just write "bank switching". If you absolutely have to shorten it, write it out fully the first time, followed by the desired abbreviation in brackets - i.e. "bank switching (B/S)".

Edited August 1, 2011 by flashjazzcat

[ClausB]

The 800's slot 2 has more select lines so this revised 48K mod needs fewer wires to the OS board:

 

Remove the OS board from its case. Remove the 74LS09 chip from the socket at Z403. Solder a 6 inch length of wire to pin 9 of socket Z403 on the back side of the board. Reinsert the chip.

 

Take the Atari 48K board and remove the 74LS30 chip from the socket at U13. Solder a short wire between pins 3 and 4 of socket U13 on the back side of the board. Now solder the wire from the OS board to pin 6 of socket U13. Reinsert the chip.

 

On the 48K board remove the 74LS32 chip from the socket at U15. Carefully bend up pins 3 and 11 so they stick straight out the sides of the chip. Solder a short wire between pins 1 and 3 of socket U13 on the back side of the board. Unsolder and lift one end of resistor R14. Reinsert the chip.

 

Wrap the long wire over the top of the OS board. Plug the OS board into the 800's slot 0 (chip side toward the rear) and plug the 48K board into slot 2 (chip side toward the rear). Remove all other RAM boards from the 800. Close it up and test for 48K RAM.

 

Schematic (red X's show disconnections, red arrows show added connections):

 

This mod is untested but I think it will work.

[kenjennings]

This looks sweet. How common are the 400 48K upgrades?

[mimo]

they are $20 from best. Don't know how many he has left though

[ClausB]

The revised 48K mod above is tested and it works!