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Bus Stuffing Demos

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Does anyone have a 4-switch or 6-switch (any model, ntsc or pal) that the bus stuffing demos fail on? I'd test mine but I cannot locate my Harmony cart atm... :sad:

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I'd test mine but I cannot locate my Harmony cart atm... :sad:

How that? My Cart never leaves the console.

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I agree, also with the Jr. But IMO that shouldn't stop BusStuffing.

 

Maybe there is a way to overcome the problem by software, which just cannot be seen right now? Or maybe the Jr. consoles can be fixed with a mod like some 7800 had to be fixed for certain Atari 2600 games? Also, the Cosmic Ark trick doesn't work right on many Jrs, still this is accepted as an incompatibility of the hardware, not the software.

 

Didn't mean to imply that work on bus stuffing should stop, only that the end result should work on "stock" hardware including the Jr. I would help test as I have a Jr. (and a 4-switch), but I don't happen to have a Harmony cart. I don't see them in the AA store, are they still available somewhere? I do have a Krokodile Cartridge, but I'm guessing it doesn't have the correct hardware inside to run this? Also I haven't used it in several years, so I'm not even sure offhand that it still works.

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Aha, I see the confusion - AtariAge doesn't sell the Harmony, they just host the site for batari. AtariAge hosts a number of other sites too, the AA Store could become overwhelmed with non-AA products if Al linked to everything else hosted by AA.

 

A search of "Harmony Cart" at DuckDuckGo (and Google, if you prefer) returns batari's site as the first no-ad result.

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I was able to collect some data using the test program that SpiceWare supplied and found that bus stuffing breaks when the Harmony is driving a logic low on a data pin, and the resulting voltage at the pin is higher than 1.39 V. This happens when the resistance between the harmony cartridge and the data bus is greater than 39 ohms. When the resistance is less than 1 ohm there is a comfortable margin of 0.47 V, at least on my four switch console. I realize that a sample size of one really doesn't provide enough data points to support a conclusion, but having a margin of nearly 0.5 V leads me to believe that bus stuffing will work on most 2600 consoles.

Noting that it takes only 39 ohms of resistance between the harmony cartridge and the data bus to break bus stuffing, it's important to have the contacts perfectly clean on both the Harmony cartridge and on the 2600 cartridge connector. I've seen oxidation on connector contacts introduce 50 ohms or more of resistance.
It's also possible, as Kosmic Stardust and ZackAttack pointed out, that some TIA chips and/or CPUs may have odd timing issues that prevent bus stuffing from working. However from what I'm seeing on the scope, the timing margins are good, and bus stuffing should work fine in most cases.

 

 

Which data pin did you collect this data from?

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Thanks!

 

I guess we shouldn't have used bus stuffing for the digits, they became useless. I'll whip up a new build in a bit, the timer just went off for my dinner.

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A 2600 Jr Rev. A. I didn't think to check the board revision when I opened it a few weeks ago. I could take a look again tomorrow.

Oh yeah, I figure I should ask this beforehand (to possibly save any unnecessary work): is the revision number usually on the top or bottom of the board?

Never mind.

Edited by TheHoboInYourRoom

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CO21503 REV E

attachicon.gifjr-board-rev.jpg

 

 

My Atari 2600 Jr REV E displays the demo properly. What's strange is the label on the board seems to be in a different location. I also tested a REF F which also worked fine. I have three other juniors, don't ask, that I haven't taken apart yet so I'm not sure their revisions. One of them didn't display properly. Unplugging and replugging the cartridge changed the results though still not correct. It makes me think the connection quality could be the issue.

 

 

post-42108-0-89575800-1487823641_thumb.jpg

Edited by netspecter

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I have three other juniors, don't ask, that I haven't taken apart yet so I'm not sure their revisions. One of them didn't display properly. Unplugging and replugging the cartridge changed the results though still not correct. It makes me think the connection quality could be the issue.

Try cleaning the Harmony Cart's connector with a Q-Tip soaked in alcohol, those connectors (bottom of reply #99) seem to get dirtier than normal for some reason. Also squish another Q-Tip, as seen in #107, soak it in alcohol and clean the cartridge port.

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My 4 switch displayed everything correctly once I got it working. My Jr. did not. Images of the Jr. running each .bin attached.

post-6479-0-56633100-1488149809_thumb.jpg

post-6479-0-44483400-1488149818_thumb.jpg

post-6479-0-29796800-1488150283_thumb.jpg

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post-6479-0-35719200-1488150304_thumb.jpg

post-6479-0-59570800-1488150315_thumb.jpg

post-6479-0-97150900-1488150328_thumb.jpg

post-6479-0-24064800-1488150339_thumb.jpg

Edited by MayDay

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Sorry don't have a pic but ran your test program through my 4 Switch and I get a black bar through #7. I cleaned both the machine and the cart and still the same result. On an interesting side not I have been testing Space Cactus Canyon from bjbest60 in the batari basic forum and I have not had any problem with the betas until ver 2.3 which crashes or restarts to title. Now Stanjr has been playing this as well and had no problems, do you think these problems could be related?

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Would the three of you please try the following test program on the systems where the previous test program failed? Instead of stuffing a 0 over a 1, it stuffs a 1 over a 0. This fixed the problem for MayDay and I'd like to see if it works for you too. If it's working correctly you should see this:

 

 

 

Sorry don't have a pic but ran your test program through my 4 Switch and I get a black bar through #7.

What a mess.

attachicon.gifpower2.jpg

One of them didn't display properly. Unplugging and replugging the cartridge changed the results though still not correct.

 

Edited by ZackAttack
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The forum is saying I don't have permission to download it.

 

EDIT: I can download other attachments in this thread just fine, even in a private window. It's just this latest ROM that I can't get.

Edited by TheHoboInYourRoom

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