Let's Improve On This - Light/Heavy Sixer ATARI 2600 w/Built-In GAMES/ROM - Hardware

I would like your help to make something awesome that we all can enjoy.

Here's the PURPOSE and POINT - -

The original ATARI 2600 had a spot on the motherboard where a built-in game was SUPPOSED to be installed:

Basically, that was a spot where an integrated circuit ROM (Read Only Memory) with a game on it, just like what you find in a cartridge, could be built-in.  Somewhere during production of the ATARI 2600, however, that AWESOME idea was scrapped, but the "solder pad" for the game remained behind.  Then, in later revisions of the motherboard that location was removed entirely.  It is only found in "Light" and "Heavy" six-switch ATARI 2600 units.

You can still install a game in that spot, though, and have it run automatically when no cartridge is loaded!  There are some limits and challenges, however.

Over the years, others have documented there observations and efforts to make this work, but to date no one has written a CLEAR, SIMPLE tutorial on how it can be done so others can enjoy it.  (I reference the work of others that I could find in more detail, below)

I'd like to change that, and I would propose that those who have something to CONTRIBUTE help write a definitive guide to make this work!

Here's my PROPOSAL - -

So far I've worked on this for a few weeks.  I have gotten it to function - - to a point!  I have major questions that are still unanswered, but I have done a lot of the first steps.

1) I would like to spell out below in tutorial format below what I have done so far.

2) And, I'd like to outline the MAJOR QUESTIONS that I think remain in order to get it to work properly

What I'd like YOU to do, if you are willing, is tackle any and all of the parts or answer questions that you feel you can CLEARLY and POSITIVELY contribute to!

What's that mean?  It means that a "drive-by spray posting" of a few phrases with no illustrations or explanation, like "well, you just tie such and such to this and that, and there you go!" are not what we're looking for.

This is for "the record," so it needs to be easy to read, and people have to be able to follow the steps again.

Try reading some of these "BACKGROUND" threads below, and you will see what I mean . . .

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BACKGROUND

There are several historic threads on the topic that provide some starting point for us.

The first is the work of AtariAge member "Longhorn Engineer" along with user "A.J. Franzman"  - -

http://www.atariage....ost__p__1301781

Take a minute and scroll through it if you would like, but to summarize, there was a lot of back and forth on what was needed to be modified or added to the motherboard, some initial versions were tried with some success, and then it was abandoned.  No real agreement on what you do or do not modify was reached.

Honestly, that was the best thread I have found so far after a fair bit of searching.

One other thread I found mentions the topic, along with a brief discussion of how to get larger games to work in that spot on the motherboard, but again no specifics are provided on how to DO it - -

http://www.atariage....ost__p__2113348

There is a quick mention of the "unicorn board" ATARI 2600 Jrs. in that last thread link I provided, where the "built-in" game made a brief manufacturing resurgence - -

http://www.atariage....ost__p__2113944

These are rare and not in every ATARI 2600 Jr. (don't start tearing yours apart!).  Some of the "features" of this board work quite well, like accommodating larger built-in games.  I have one of these boards and have gotten it to work with a built-in game (I chose PITFALL!), as I start to detail here - -

http://www.atariage....-compatibility/

And, other topics can be found about "unicorn boards" as well - -

http://www.atariage....2600jr-unicorn/

http://www.atariage....-unique-2600jr/

It's relevant because some of the "switching circuitry" that allows this to work in these late-model ATARI could be useful for this project.

[Do you have other links or references for this section?  Contribute them if you do, please!]

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QUESTIONS

Some of these questions won't make sense until you start reading the outline of the TUTORIAL below but it's good to get them out here first, I think.

There are just THREE main questions right now:

- How SPECIFICALLY (what is soldered where and why) is it possible to get games larger than 2k to work in the solder spot?

I have installed several 2k size games into the spot on a Light sixer, and had them work (COMBAT, etc.) but anything larger, like DONKEY KONG, will not work.

As mentioned above, "A.J. Franzman" alludes that it is possible (http://www.atariage....ost__p__2113348), but there are no details.

I can tell you that a 4k game DOES work in the "unicorn" - - PITFALL! is 4k, and I was able to get DONKEY KONG to work, too.

- What is the BEST way (again, with as much detail as possible with what gets modified or added and why!) to get maximum compatibility for the detecting and automatic switching of a cartridge being loaded?

I am pleased to say that by just straight installing a 2k ROM integrated circuit in the solder spot and doing NOTHING else, you actually get a LOT of compatibility.  The console will automatically switch to the loaded cartridge in many situations.  But not all.

I have not figured out a pattern.  Here's an interesting list of games that DID boot and work with the built-in ROM in place (non-scientific, I was just grabbing carts from a box) - -

KEYSTONE KAPERS, DECATHALON, YARS' REVENGE, PRESSURE COOKER, COMBAT, FROGGER, WIZARD OF WOR

And, those that did not - -

GRAVITAR (you see the title screen, and then it rolls and glitches out), SPACE SHUTTLE, PITFALL II, and the HARMONY CARTRIDGE

The HARMONY is a known case, and is likely fixable, by the way - -

http://www.atariage....70#entry1943270

But, I have tried shorting those two pins that were mentioned, and still can't get it to work.

Once the ROM is pulled from the motherboard, ALL of the above games will work just fine, including the HARMONY, by the way.

- What is the cleanest and most direct way (once more, with DETAIL on exactly what to cut and solder!) to wire in a "kill switch" for when the above "compatibility mods" don't always work?

We need a way to absolutely and positively disable the on-board built-in ROM for times where you want to return the console to its native state.

I have looked and looked, and I just don't understand enough about disabling ATARI mask ROMs.

I think it will involve cutting some traces that go to the place where ROM is located on the motherboard, wiring some pins of the ROM to be able to be grounded (or electrified?), and putting a positive switch in there somewhere that gets flipped.

Any and all ideas on this one are welcome!

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TUTORIAL

This will be short and sweet - - the steps thus far are simple!

Take apart your sixer and expose the motherboard.

I used this light sixer, with this serial number, and a manufacturing date of August 14, 1980 - -

Ugh, this one was kind of gross before it got cleaned, and someone had kludged in a random non-ATARI cable - -

Here is the motherboard and revision number - -

And, as shown before, the solder spot - -

I simply cleaned the solder holes with soldering braid, and then soldered in an integrated circuit socket - -

IMPORTANT - - note that the socket is BACKWARDS the way I installed it! The "key notch" that shows you which way to orient the integrated circuit when you socket it in is reversed!

I learned this because on the UNDERSIDE of the motherboard is a VERY small "1" etched into the traces that tells you where the first pin of the integrated circuit should go - -

Look in the upper left hand corner, near my "1" that is drawn in marker (IGNORE my wire coming off the pin in this picture, it's something I was doing for testing)

Now, in order to install your ROM, I recommend you actually place it in ANOTHER socket, and you will be socketing THAT socket into the one that is soldered on the board. I do this so I can have some modularity with my ROMs, and swap and try different ones.

Here's how that looks - -

I actually place a dot of solder at each of the four corners of the socketed ROM so that it doesn't come back out, too.  If you are swapping these things in and out of the motherboard, it can happen, so this just secures it.

What ROM to use?  Right now there is a 2k ROM size LIMIT!  If we can figure it out, the maximum size is 4k.  No bankswitching or fancy special chip ROMs will be possible.

EEPROMs are possible with the inclusion of an inverter [This is a section that needs to have more input on exactly WHERE and how an inverter would be placed to allow for an EEPROM]

How do you know?  I used Kevin Horton's excellent list of cartridges and scanned down it for 2k ROMs - -

http://www.emulatron...tari8/sizes.txt (direct link)

Which was found here - -

http://emu-docs.org/...=All%20Consoles

NOTE: desoldering ROMs from cartridges is slow and laborious.  Desolder EVERYTHING completely though, and go slow so that you don't hurt the pins on the ROM!

And, once you have your ROM and have socketed it, then you can place it on the board.

NOTE the proper direction and orientation of the "key notch" here, which is facing RIGHT! - -

DO NOT press down all the way with your socketed ROM!  Just enough to make contact is for testing is perfect!  If you press it in all the way, it's going to be HARD to get it back out without possibly bending pins!

Once you are certain the project is done, you can "click" it positively in, however.

And, that's it.

Really.

Turn on the console with no cartridge in it, and COMBAT or whatever will boot.   Put a game in the cartridge slot and it will likely boot - - depending on the game.

Now, there was a lot of talk in that thread referenced above about cutting ground traces, adding in a zener diode, and other "pull up circuits."

I tried all that.  I also tried it all WITHOUT it.  So far, it works the same EITHER WAY, compatibility bugs and all.

(note my zener diode and the cut trace on the ground, just like "Longhorn Engineer" had)

Now I have repaired the cut trace, and removed the zener diode - - and I have the same exact compatibility as I did before. This is how it is operating now.

I think that the "answers" to some of the compatibility questions and the kill switch idea will require cutting traces, but for now, this "works" without it.

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SO, that's where I am at.

Still with me?

tl;dr ? (too long; didn't read?)

I'm looking forward to any and all ideas that people have. I will happily cut and solder whatever, as long as there seems to be a decent reason behind it, so please feel free to make suggestions!

-atari2atari

atari2atari, on Sat Apr 14, 2012 8:57 AM, said:

Looks like I have lost my ability to edit the first post - - too bad!

I mean to include this "snip" of the 2600 schematics that shows the place where the ROM is also mentioned - -

Attachment

Snip from 2600 Schematics.JPG

Now, on to your questions . . .

SoundGammon, on Fri Apr 13, 2012 10:28 PM, said:

...I'm just going to toss this idea in to the wind, but have tried an eprom instead? Maybe a 2516 or a 2716 eproms for 2k and 2532 or 2732 eproms? Just a thought...

Great questions on EPROMs!

From what I know so far - -

- EPROMs will theoretically work, although I have not personally tried it

- The same 2k or 4k limit applies, with no bankswitching, etc.

- EPROMs have the same pin-out as an ATARI mask ROM, with the exception of . . .

- EPROMs are "active low", which means that a low voltage current to the right pin on the IC will enable the EPROM. ATARI mask ROMs are "active high", so a high current (+5 v, I think) to activate the chip. This means that there is a high current on the motherboard headed to the chip select pin (remember, they have the same pin-out) that needs to be inverted so that the EPROM can be used.

Pioneer4x4, on Sat Apr 14, 2012 6:53 AM, said:

Very interesting work so far.
As I mentioned in another thread. I would mount an inverter between 2 sockets and wire it up by bending pins so they do not pass through. Then you could use it as an adapter for EPROMS. Is there any space limitations above it?

Would you mind showing us in pictures exactly where you would wire that inverter, and specifically what part number or type of inverter you would use? "A.J. Franzman" also mentioned that you could use an inverter, but never provided details - - http://www.atariage....ost__p__2113850

I would be great if you wanted to provide some concrete details, and then I could try it out!

Here's some handy pictures for your use - -

-a2a

Pioneer, the above question is still relevant, and if you can answer it, that's great, but perhaps this would assist your illustration or wiring diagram?

http://www.atariage....ost__p__2066625

-a2a