Atari 2600 Game Incompatibilites

[Tempest]

I'm thinking about putting my 2600 away and just using my 7800 as the S-Video mod is much nicer and I'm low on space.   My biggest worry is that there are 2600 games that don't play correctly on the 7800 due to various timing differences.  Growing up I had a 2600 jr and I remember running into several weird gameplay issues like Millipede not moving past the bonus round unless you died during it (it would just sit there) and some games having graphical glitches.  I tested several and didn't see those issues thankfully, so maybe my 7800 is more compatible than I thought.  I even tested the Anteater prototype which is known for having the 0's in the score overlap due to timing issues on the jr and my 7800 displayed it properly.   Of course there are the ones that everyone knows don't work (Robot Tank, Decathlon, etc.), but those have all been patched so those are no longer an issue.  The ones I'm wondering about are the games that do appear to work, but have various gameplay glitches that show up later on and might not be noticeable right away.  Is there a list of games that I should check?

 

 

[+-^CrossBow^-]

I believe I disabled the C64 cap on your 7800 to improve 2600 game and home brew compatibility. For instance the bus stuffing techniques should work on it. There are two games that I know can be affected by this. One of them I tested with yours afterwards and it still worked. That game being the 2600 version of Dark Chambers. That is usually the main game that no longer works when disabling the extra timing circuit, but on yours that game still worked properly. However, another game that seems to always be affected by this change, is the 2600 version of Kung Fu Master. I've heard it can affect the 2600 version of Double Dragon as well, but I've not seen that myself. 2600 Kung Fu Master so far, will NOT work properly on 7800 consoles with the timing circuit disabled.

 

However, you should test Robot Tank, and Decathlon as they likely will work since they tend to work with the extra timing disabled. But as you stated, there are versions that you can load up on Harmony or other carts that work around this.

 

So to begin a list based on what I've personally checked:

 

Most post '84 design 7800s that are stock have issues with the following 2600 games:

- Activision Space Shuttle

- Activision Robot Tank

- Activision Decathlon

- Some homebrews (but I've not tested this indepth since I don't own that many actual homebrew games)

- Spiceware's bus stuffing demos (Parrot demo is the main one I use to test)

- Supercharger games (Communist Mutants locks up, Frogger has missing sprites) 

 

Post '84 design 7800s with timing circuit disabled may have issues with the following 2600 games:

- Kung Fu Master - This is assured to not work in my testing

- Dark Chambers - Usually won't work but some 7800s still manage to pull it off

- Double Dragon - I've not personally seen an issue with this game but it has been reported by others to be affected.

- Stargate/Defender II (I've never seen an issue with this game but it has been stated as being possible)

 

That is just from what I've personally seen from the 7800s I've had pass by me. But with so many variants on the revisions and how 7800s were made, this is just a guideline list from me.

 

[Tempest]

27 minutes ago, -^CrossBow^- said:

Post '84 design 7800s with timing circuit disabled may have issues with the following 2600 games:

- Kung Fu Master - This is assured to not work in my testing

- Dark Chambers - Usually won't work but some 7800s still manage to pull it off

- Double Dragon - I've not personally seen an issue with this game but it has been reported by others to be affected.

- Stargate/Defender II (I've never seen an issue with this game but it has been stated as being possible)

 

That is just from what I've personally seen from the 7800s I've had pass by me. But with so many variants on the revisions and how 7800s were made, this is just a guideline list from me.

 

All those games work, even Kung Fu Master (I got to the first boss, but he killed me).  Are there specific things I should be looking for?

[+-^CrossBow^-]

37 minutes ago, Tempest said:

All those games work, even Kung Fu Master (I got to the first boss, but he killed me).  Are there specific things I should be looking for?

Then you really do have a very compatible 7800! Even my daily driver won't play 2600 Kung Fu Master since I disabled the timing circuit on it. All others I've tested after doing that, wouldn't work either but then again, yours is also able to still play 2600 Dark Chambers as well so go figure?

 

As for what the look for? Well in the case of Kung Fu Master, it just loads up to a black screen on a 7800 with the timing circuit disabled in most cases. Same with Dark Chambers. 

 

 

 

 

[Tempest]

20 minutes ago, -^CrossBow^- said:

As for what the look for? Well in the case of Kung Fu Master, it just loads up to a black screen on a 7800 with the timing circuit disabled in most cases. Same with Dark Chambers.

Nope it works.  Crappy as ever. 

 

[+-^CrossBow^-]

3 minutes ago, Tempest said:

Nope it works.  Crappy as ever. 

See you bring up a good point here. Are the games I've listed as possibly getting broken by the slight modification worth the cost for the ones that come back to life in the process?

 

[Lord Innit]

Both my Haunted  House carts don't work properly in my 7800.  The eyes appear on the left side of the screen.  

[Tempest]

31 minutes ago, -^CrossBow^- said:

See you bring up a good point here. Are the games I've listed as possibly getting broken by the slight modification worth the cost for the ones that come back to life in the process?

 

Well Stargate and Dark Chambers are.  DC is alright but Stargate is one of the best games on the system.

[Tempest]

3 minutes ago, Lord Innit said:

Both my Haunted  House carts don't work properly in my 7800.  The eyes appear on the left side of the screen.  

I don't have a copy to check out unfortunately.  I don't have many homebrews.

[Lord Innit]

I meant Atari's  Haunted House from 1982

Just now, Tempest said:

I don't have a copy to check out unfortunately.  I don't have many homebrews.

 

[nadir]

9 minutes ago, Lord Innit said:

Both my Haunted  House carts don't work properly in my 7800.  The eyes appear on the left side of the screen.  

Oh, never heard of that one before.  My Haunted House cart works fine on my 7800.  I don't recall if it worked prior to modification, but definitely works post-Robot Tank mod.

[Lord Innit]

2 minutes ago, nadir said:

Oh, never heard of that one before.  My Haunted House cart works fine on my 7800.  I don't recall if it worked prior to modification, but definitely works post-Robot Tank mod.

I started a thread a few years ago about this issue. I now have a harmony cart with a fixed ROM.

 

[+-^CrossBow^-]

14 minutes ago, Lord Innit said:

I started a thread a few years ago about this issue. I now have a harmony cart with a fixed ROM.

 

UK systems don't seem to benefit from disabling the extra timing circuit like the NTSC consoles do. What I can tell you about this small mod that I find interesting is that the games themselves are actually loaded up and working fine. I know this because if I put a switch on the capacitor to enable/disable the connection. I can leave it disabled and then turn on a game like Kung Fun Master and get the blank screen condition because again, I have the extra timing disabled. I can literally flip the switch in the Enable position and the game graphics suddenly come up and the game works. Same with other games I've tested. Now the opposite side of this, is that to use Kung Fu Master as an example again, I can leave the switch in the enable position, power on the 7800 and the game comes up and works as normal. I can then disable the circuit and in some cases, the game will continue to stay up and running without issue? But with Dark Chambers, it will usually got a black screen as soon as I disable the circuit. 

 

The point is that the extra timing circuit seem to have more to do with the video signal startup vs the actual game since it seems the games are actually running and we just can't see them.

 

[Tempest]

I still find it odd that Atari went through all that trouble and expense just to get Dark Chambers working.  You think it would be easier to just slap a "Not compatible with the 7800" sticker on the box and be done with it, especially given how shoestring everything was at Atari at the time.  There must be more to it than that.  I wish we had some internal documents about this that could shed light on it.

[+-^CrossBow^-]

Just now, Tempest said:

I still find it odd that Atari went through all that trouble and expense just to get Dark Chambers working.  You think it would be easier to just slap a "Not compatible with the 7800" sticker on the box and be done with it, especially given how shoestring everything was at Atari at the time.  There must be more to it than that.  I wish we had some internal documents about this that could shed light on it.

More confusing is that Atari did away with the extra timing circuit on later built 7800s. So it appears to have been a thing mainly during the '87 - '88 build years. I've wondered if it had to do with the different speeds of ram they were using? I tend to see the circuit mostly on 7800s that have slower speed RAM in them. However, this last one I did, had 12ns Oki RAM in it and had the cap for C64 installed but didn't have the rest of the ICs chips installed for it?! It also didn't have the bodge resistor coming off the bottom ram chip's WE line to ground as I've seen on quite a few Sony RAM chips. So.. I honestly do not know why it exists or doesn't but I have to believe it is related to the rest of the components used in the main boards at the time. Like maybe something they needed wasn't quite available at the rated specs, so they did something to compensate for it in some way? Again, in most instances, the games are actually still running and it is just affecting the video output. 

 

Darrel's parrot bus stuffing demo is fun to test with because with the extra timing in place, it will be a scrambled looking mess on the screen. Disable it, and the picture immediately comes in without power cycling the system. You can do the same in reverse with leaving it disabled when powered on and then enable the timing circuit and the picture will go crazy. It is one of the rom files I've found that will instantly be affected by this without power cycling the systems. I've only messed with this a little on a few 7800s here and there.

 

 

[RevEng]

The Haunted House issue isn't really a 7800 compatibility issue. HH has a code bug that accidentally loads a value from TIA instead of using a constant value. This is literally a goof-up on the programmer's part. On most consoles the game works despite the code bug, because those consoles have enough bus capacitance to give previously read values some hang-time, if the bits in question remain undriven.

 

However this isn't expected or guaranteed behaviour. Some seemingly rare consoles don't have sufficient hang time to overcome this sort of code bug, including 2600s. I haven't seen any evidence that the 7800 is more or less prone to the issue than the 2600 is, though admittedly the rarity of these consoles makes the comparison a bit tricky.