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MrPix

AY-3-8915 to RGB adapter.

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Someone asked me about the possibility of designing an RGB adapter for the AY-3-8915. It looks almost trivially simple to do. What am I missing?

 

In the table below, it looks like I just need to recreate the table using RGB values as an alternative output, and put that 3:3:3 or 4:4:2 output through three R2R ladders. Synch can be produces as H, V and CSYNCH too. From there, it would be easy to derive CLEAN composite, or S-Video output too.

Would there be much demand for this?

I did see someone else's very overly huge RGB adaptor by googling. I would be able to make something 1/4 the size of that. It would be economical.

Screen Shot 2020-05-21 at 7.30.10 PM.png

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Would this be an RGB video mod for the Intellivision?  If so, I'm interested.  I guess I'm interested anyway since anything with that IC in it could produce RGB signals.

 

Have you every looked at the Fairchild Channel F, Atari 7800, Emerson Arcadia 2001, or Bally Astrocade and considered RGB mods for those?  I'm very interested in RGB mods for all of those.

 

For any systems with an RGB mod I'd also like an option for composite and s-video.

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I’m interested in all of it, if I can get the hardware cheaply. Also memory and carts too. I have tons of rom and sram. 

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I'd be interested, the previous RGB mod that existed for the INTV is no longer available (AFAIK) and also isn't compatible with upscalers like the OSSC or Framemeister.

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Do you know what made it incompatible?

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I only know that it seems much more difficult to do a RGB mod on a NTSC Intellivision than on a PAL one. But it has been done. 

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I would be quite interested. There are a few different composite mod kits out there but they are all based on the same initial scheme that is in the wiki with some differences being used in the values of the components.

 

The main issue I think you will run into is that not all intellys are the same. As an example, I've installed the same composite mod board into different intellivision model 1 units like the Sears SVA and standard Intelly 2609 and get different results from them? Some Intellivisions with the current composite mod kits will also produce the wrong colors through composite but look correct through RF and it has been quite frustrating to have to keep several different kits on hand to test them all to find one that has good colors, but then it has bad color bleeding around contrasting colors, or some games look correct color wise but then you pop in something like Armor Battle and the water is pinkish in color instead of blue? 

 

For me personally, I find that s-video is plenty for me on these older systems. I can understand the want for true RGB and I do have the means to use it and have a few systems setup on it. But they are much newer systems that I think take better advantage given their higher resolution and larger amount of colors on screen as compared to these older 8-bit systems.

 

So for me at least I'm all in for a more consistent composite and s-video solution!

 

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2 hours ago, Intymike said:

I only know that it seems much more difficult to do a RGB mod on a NTSC Intellivision than on a PAL one. But it has been done. 

Well, of course! The sync and color burst system is beyond ridiculous. :D 

1 hour ago, -^CrossBow^- said:

I would be quite interested. There are a few different composite mod kits out there but they are all based on the same initial scheme that is in the wiki with some differences being used in the values of the components.

I'm not targeting a console as much as a device - the AY-3-8915. If that's in the console, my proposed board will create crystal clear RGB at the same timings, which then is the ideal source signal to create clean S-Video or new composite. Most of the improvement in video quality comes from using 'modern' components on a 4-layer board.

1 hour ago, -^CrossBow^- said:

The main issue I think you will run into is that not all intellys are the same. As an example, I've installed the same composite mod board into different intellivision model 1 units like the Sears SVA and standard Intelly 2609 and get different results from them? Some Intellivisions with the current composite mod kits will also produce the wrong colors through composite but look correct through RF and it has been quite frustrating to have to keep several different kits on hand to test them all to find one that has good colors, but then it has bad color bleeding around contrasting colors, or some games look correct color wise but then you pop in something like Armor Battle and the water is pinkish in color instead of blue? 

*grins* I've experienced this problem - which is why I bypass the whole thing and just find video ICs where I can effectively replace the IC's functionality rather than reforming its outputs. Luckily, the 8900 and character ROMs etc. do their thing and the video generation on the 8915 is a simple 5-bit code with a "white overlay" - I can use a small CPLD to re-implement the logic entirely and output clean 3:3:2 RGB to make the 16 colors and all sync signals. Frankly, the hardest part of this is that each user has experienced different colors so they have their own fixed ideas of what the colors should be. That's why I posted here asking for help to create an RGB conversion table ;)

1 hour ago, -^CrossBow^- said:

For me personally, I find that s-video is plenty for me on these older systems. I can understand the want for true RGB and I do have the means to use it and have a few systems setup on it. But they are much newer systems that I think take better advantage given their higher resolution and larger amount of colors on screen as compared to these older 8-bit systems.

 

So for me at least I'm all in for a more consistent composite and s-video solution!

*nods* That's my goal. Consistent, crisp, bright but not over-saturated video, no dot crawl, no ripples or ghosting or jailbars, but that meets the original frame rates and resolutions.

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Here's a little chart I derived of possible RGB values for the 16 8915 colors. I have looked at a bunch of screenshots and Youtube videos and approximated as best as I can.

If you can look at them and suggest improved RGB codes, I'd appreciate the feedback :D 

Screen Shot 2020-05-22 at 11.43.58 AM.png

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18 minutes ago, MrPix said:

Here's a little chart I derived of possible RGB values for the 16 8915 colors. I have looked at a bunch of screenshots and Youtube videos and approximated as best as I can.

If you can look at them and suggest improved RGB codes, I'd appreciate the feedback :D 

Screen Shot 2020-05-22 at 11.43.58 AM.png

I'm going to send you a PM on this that might be helpful although you likely have done this already...

 

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Good morning
Since I am having problems with the 1591 pal model (to make a rgb mod), any help, since there are no electrical diagrams of that console on the internet, would be very useful. Unfortunately, I'm too far away from you to ask for your help directly. If, kindly, you have some input to give me (even in private), I would be very grateful to you. Sorry for my english

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The module I am designing will work on NTSC or PAL models, as long as they have an AY-3-8915 IC.

My project will be open hardware, and I will release all files, JEDECs and PCB files. I normally do this about three months after I release items, so I have a bit of time to recover my development cost.

So yes, all this info will be public. :)

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The one possible down side is that there is a line for an external video feed from the cartridge port.  So if any of the cartridge port devices fed video, they would not work with this scheme.  On the other hand, I have no idea if this external feed was ever used.

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The 8915 has 280nS pixels. It also has a video input pin to overwrite white text at 120nS pixels. I'm incorporating this logic, so this will work correctly. I don't know if anything used it either.

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Posted (edited)

It's the ay-3-8900-x stic chip that outputs the five bit colour/sync code not the ay-3-8915.  So you could make pal and ntsc versions. Pal intellivisions don't have an 8915 chip.  Most PAL intellivisions, unlike ntsc ntellivisions, have a custom chip that outputs a digital rgb signal that some rgb mod kits made use of.

 

The keyboard component and system changers makes use of the cartridge port video inputs. The 8915 video input is not used. And the intellivoice sends audio through the cartridge port.

 

Regarding colours, here's an internal mattel document that has the yiq colour information sent to their hong kong manufacturer.

http://papaintellivision.com/pdfs/CCF10242011_00001.pdf

 

And here's an atariage discussion on colours.

https://atariage.com/forums/topic/278354-gfx-palette-flag/

Edited by mr_me

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15 minutes ago, mr_me said:

It's the ay-3-8900-x stic chip that outputs the five bit colour/sync code not the ay-3-8915.

That's true, but the white high res video signal is at the 8915 socket and isn't available at the STIC. I'm not aware of anything that uses it in the Intellivision, but the 8915 was used in other systems so I have to account for those that might have used high res white. Looking at the schematic, that signal can come from the cartridge port.

15 minutes ago, mr_me said:

So you could make pal and ntsc versions. Pal intellivisions don't have an 8915 chip.  Most PAL intellivisions, unlike ntsc ntellivisions, have a custom chip that outputs a digital rgb signal that some rgb mod kits made use of.

My board will not care about the format of what's being input. It's good to know that some PAL systems might not have a PAL socket, and I might need to make a little adapter board to pick up those signals. Thanks for the heads up. I love when knowledgeable people in the community save me from pitfalls and traps like this ;)

15 minutes ago, mr_me said:

The keyboard component and system changers makes use of the cartridge port video inputs. The 8915 video input is not used. And the intellivoice sends audio through the cartridge port.

 

Regarding colours, here's an internal mattel document that has the yiq colour information sent to their hong kong manufacturer.

http://papaintellivision.com/pdfs/CCF10242011_00001.pdf

 

And here's an atariage discussion on colours.

https://atariage.com/forums/topic/278354-gfx-palette-flag/

Excellent info. Thank you. Snagged and archived in my dev folder. :D

You folks are awesome!

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Posted (edited)

According to the 2609 intellivision schematic the 8915 video input is only connected to ground.  And the cartridge port video input mixes with the composite video feeding the rf modulator.  The Intellivision II actually uses a different cartridge port pin for external video.

http://spatula-city.org/~im14u2c/intv/tech/master.html

 

edit:

I wouldn't worry about external video but you have to pick up external audio for intellivoice support.

Edited by mr_me

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47 minutes ago, KylJoy said:

Here's how I plan to solve that problem.

I will set up a counter that measures the time between the synch signal rising edges. This would be half clock accurate as the output is clock /2. When the sync is present I would use it to reset the counter. When the sync is absent, the counter will generate the synch signal. This way, the synch signal will always be present and the OSSC should be able to lock onto it. This gives us a counter generated, /2 clock accurate clean synch. Boom!

This will work automatically for NTSC and PAL timings too.

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Hello,

Interesting.

I had exactly the same idea. As ramdacs are all obsolete and as I don't want to base a design on "new old stock" or refurbished ebay/aliexpress parts, my plan was to use a small CPLD or FPGA and a still active video dac like ADV7125/3.

As I want the design to be fully open even at the toolchain, I go for FPGA, a Lattice iCE40 (LP8K) and protyping with a TinyFPGA BX. A MachXO with 5v tolerant pin and integrated Flash is more appropriate but is a no go for me.

It seems a little overkill as a first though, as it complicate things (level adaptation etc ...) but could be a generic base for many converters. The stocks of music ramdac used in Tim 2600 RGB board will not be avaible eternally.

I had targeted the Intellivision first, but I will use the extras in the FPGA for my "universal 2600" project which will drive programmable clock, button rewiring etc... with a soft core or with the help of a little µC.

For the intv, the pll could help to regenerate and tune a clean hsync from scratch.

But as I am very slow at completing my projects, you definitively will have something working before me 😊

 

 

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I’m planning to downrange with the very minimal ATF150X family. Super cheap and more than up to the task. 
 

If you want, we can combine projects. If not, that’s fine too. 

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Personally, it would be better to skip the OSSC and either go straight to component or get an HDMI chip to have an all-in-one upgrade board.

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I would really appreciate a fix for the INTV RGB board to work with the OSSC.

 

I'd also love a new board that would give component, RGB, s-video and composite!

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