Expansion Interface installation

[+DrVenkman]

You're probably right but I still kind of hope @CPUWIZ's tease will eventually result in SOME kind of fun gadget, even if only a proof of concept. 

 

And aside from DRAGON'S LAIR/FIREFOX type LD titles, I still think shooters in the vein of VANGUARD and similar would benefit. Put a scrolling, very colorful high-res video file behind MARIA sprites, with music streamed in from the player and POKEY/TIA/YM/whatever sound effects and musical accent cues. 

[alex_79]

9 hours ago, Lynxpro said:

 How does synching not count as I/O if it's bidirectional by nature?

In order to communicate with an external device (e.g. a savekey), you need inputs and outputs that can be seen and controlled by the CPU. The program running on the 7800 must be able to read from an input pin and write to an output one.

By looking at the schematic, the expansion port doesn't provide any of that.

 

If bidirectional communication between the external device and the 7800 is required, it doesn't (it can't) happen through the expansion port. There needs to be some additional connection between the two, using the cart and/or controller port.

By using the expansion port alone, the external device can only:
- halt the cpu and disable Maria - highlighted in purple in the attached schematic.
- provide the clock to the 7800 (as they must use the same clock to ensure synchronized video outputs that can be mixed together) - magenta in the schem.
- see the A/V output from the Maria chip (including the separate digital luma, color and video sync signals) - green.

 

All of this happens on the hardware level, and there's nothing else there. I don't see anything on the expansion port that can be controlled/seen by software running on the 7800.

 

[+x=usr(1536)]

11 hours ago, DrVenkman said:

And aside from DRAGON'S LAIR/FIREFOX type LD titles, I still think shooters in the vein of VANGUARD and similar would benefit. Put a scrolling, very colorful high-res video file behind MARIA sprites, with music streamed in from the player and POKEY/TIA/YM/whatever sound effects and musical accent cues. 

Thinking out loud about it, this may be doable with technology we already have available - attach a DEXTER and you're about 80% of the way there.

 

The porting involved would be very interesting.  In the case of games using timing-based moves (Dragon's Lair, Space Ace, Cliff Hanger, et. al.), it would likely be necessary to use the original game's data.  Player / DEXTER control would have to be based on its own engine, but that should easily be within the 7800's capabilities.

 

Overlay games like Astron Belt, Galaxy Ranger, Interstellar, and so forth would require a bit more of an engine since sprite tracking and collisions would be part of the equation, but that's not impossible.  Where it would conceivably become tricky would be with games like M.A.C.H. 3 and Us. vs. Them - they stream target data from one of the audio tracks on the disc back to the game for collision calculations, etc.  Still, that could conceivably come from a cartridge.

 

Very interesting.  Potentially, not all LD titles would be candidates for a port, but it seems as though a large percentage of them could be.  The MSX managed to do it, so can't really think of a reason why the 7800 wouldn't be able to handle it as well.

[+slx]

On 6/21/2022 at 8:55 PM, Muddyfunster said:

On PAL 7800's the RF is horrific, even on a CRT (at least mine was anyway). Maybe I just had a console with a duff RF but it was pretty gnarly.

I have a PAL unit which (to me) looks quite decent on a B&O TV.

[Lynxpro]

On 6/30/2022 at 2:35 AM, alex_79 said:

In order to communicate with an external device (e.g. a savekey), you need inputs and outputs that can be seen and controlled by the CPU. The program running on the 7800 must be able to read from an input pin and write to an output one.

By looking at the schematic, the expansion port doesn't provide any of that.

 

If bidirectional communication between the external device and the 7800 is required, it doesn't (it can't) happen through the expansion port. There needs to be some additional connection between the two, using the cart and/or controller port.

By using the expansion port alone, the external device can only:
- halt the cpu and disable Maria - highlighted in purple in the attached schematic.
- provide the clock to the 7800 (as they must use the same clock to ensure synchronized video outputs that can be mixed together) - magenta in the schem.
- see the A/V output from the Maria chip (including the separate digital luma, color and video sync signals) - green.

 

All of this happens on the hardware level, and there's nothing else there. I don't see anything on the expansion port that can be controlled/seen by software running on the 7800.

 

 

Most untriumphant. Thanks for the explanation and the diagram.   

[Ecernosoft]

On 6/21/2022 at 5:19 PM, DrVenkman said:

My Sears Heavy Sixer has marvelous RF, and my Light Sixer is almost as good. My later-made 4-switch units have gross RF. One of my 5200's had okay RF but I've put a UAV into that one as well. 

My 7800 delivers almost composite-quality RF. It's really that good! (Note- on my 2007 HD TV which miraculously uses good RF filters it looks even better!)