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Intellivision ntsc rgb mod design help


emerson

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Good to hear. I will be working on a similar project in the near future using different components namely a FPGA, ADV7125.

Anyway I don't know if I skimmed over it but have you tried taking sync from the bits 1 X X 0 1 instead of wherever you are taking it ?

I just wonder if one is better than the other; it could possibly save me a lot of grief in the future.

 

I think in general using C-sync instead of sync on xxx is better. Also if you use those bits you could use the THS7374 on the outputs (SRGB) to easily toggle C-Sync 75 or C-Sync TTL with just resistors and jumpers.

The lm1881 can then be done away with entirely. I can go way more into detail if needed.

 

When you say "bits 1xx01" I assume you mean V5-V1 from the AY-3-8915 correct? Looks like it based on the datasheet. I decided to pull sync directly from the composite video signal in an attempt to ensure compatibility with the OSSC. Fred's mod seems to derive it's sync signals based on V5-V1 but somewhere there is a timing issue. My circuit monitors V5 and blanks the screen whenever it goes high. It does not specifically look for the "1xx00" blank condition from the AY-3-8915 truth table.

 

 

Also I dunno if it helps but the external video is half the length of RGB on the same rising edge (I believe)., which is specific to the intellivision 1. I have no idea what the others do.

At any rate that signal should be a square wave input that is 1111-1111, 255, aka white. I don't know anything about the device you are using or programable circuits in general (yet).

 

Not to be rude but I have no idea what you're talking about here. Can you please elaborate?

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When you say "bits 1xx01" I assume you mean V5-V1 from the AY-3-8915 correct? Looks like it based on the datasheet. I decided to pull sync directly from the composite video signal in an attempt to ensure compatibility with the OSSC. Fred's mod seems to derive it's sync signals based on V5-V1 but somewhere there is a timing issue. My circuit monitors V5 and blanks the screen whenever it goes high. It does not specifically look for the "1xx00" blank condition from the AY-3-8915 truth table.

 

 

 

Not to be rude but I have no idea what you're talking about here. Can you please elaborate?

 

Yes blanking on 1 is a must. I don't get what you mean by composite ? Would that be a mod kit or do you mean just the ORing of H and V sync aka C-sync?

Looking at the datasheet H and V sync have different values for the resistors. I would expect them to be the same value but idk.

You could try ORing those two for C sync. those outputs ORed should be the same functionally as the output of the lm1881 but much cheaper.

Anyway I don't understand why a version using the bits would be worse. Ill find out soon enough. Thanks.

 

There is another video input signal on the intellivision 1 for the keyboard component.

From the AY-3-8915 Datasheet:

 

The required color to be displayed for each 280ns PIXEL is

decoded on a four line binary coded input. This selects one of

sixteen possible colors. An external resistor network completes

the D to A function as shown in the schematic of Fig. 1. The

waveform pi us table illustrates the use of the five inputs to produce

composite sync, color burst, line blanking, frame blanking and

video.The external video input pin provides the ability to superimpose

white high resolution (140ns wide) video information over the

picture (color image).

 

By 1111-1111 I mean 714mv or 1.428v (unterminated) meaning that external video input would be that same as white but at half the length. Aka 0111. V5=0 V4=1 V3=1 V2=1 V1=1

I don't know the limitations of what you are using but a FPGA would be able to superimpose by ORing say 1111-1111 and 0000-0000 (or any other value) across all rgb lines for 140ns.

Part of the confusion is probably that im dealing with the decimal or binary you are probably looking more at the voltages.

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When I say composite I mean the composite video mod in my circuit. I too would expect the hsync and vsync resistors to be the same. Not too sure what's going on there either...

 

I didn't mean to imply ORing hsync and vsync is worse than pulling sync from the video signal. All I'm saying is the firmware in Fred's rgb mod doesn't work with the OSSC so I decided to take a different approach.

 

My circuit works by taking the 5bit code on V5-V1 and expands it to 9 bits, or 3 bits for each red green and blue and runs that through a 2:1 resistor ladder. The bits and voltages aren't the issue. The problem is I forgot about the external video input on the cartridge port. I honestly couldn't say how my circuit behaves with it since I don't have an ECS to test with. Based on the datasheet description it seems like the AY-3-8915 superimposes the external video for you. How else would the external video get placed on V4-V1? My guess is the AY-3-8915 generates a 140ns "0111" state on V4-V1 when the external video pin gets toggled but this is just speculation. I wouldn't think the external video input would be analog, especially just for one color. It would have to start as analog, get converted to the 4bit color code then back to analog. That seems a little backwards but I could be wrong.

 

I'm using a GAL22V10 which is an older programmable logic chip. In the programming software I was able to set up a truth table of color code inputs and decoded outputs so hopefully you can do something similar with your code. It makes adjusting the color palette a breeze. Since you're going with a 24bit rgb color code you'll be able to directly port color palettes from jzintv which will be cool. Do you plan to have a program header so people can customize their palettes?

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When I say composite I mean the composite video mod in my circuit. I too would expect the hsync and vsync resistors to be the same. Not too sure what's going on there either...

 

I didn't mean to imply ORing hsync and vsync is worse than pulling sync from the video signal. All I'm saying is the firmware in Fred's rgb mod doesn't work with the OSSC so I decided to take a different approach.

 

My circuit works by taking the 5bit code on V5-V1 and expands it to 9 bits, or 3 bits for each red green and blue and runs that through a 2:1 resistor ladder. The bits and voltages aren't the issue. The problem is I forgot about the external video input on the cartridge port. I honestly couldn't say how my circuit behaves with it since I don't have an ECS to test with. Based on the datasheet description it seems like the AY-3-8915 superimposes the external video for you. How else would the external video get placed on V4-V1? My guess is the AY-3-8915 generates a 140ns "0111" state on V4-V1 when the external video pin gets toggled but this is just speculation. I wouldn't think the external video input would be analog, especially just for one color. It would have to start as analog, get converted to the 4bit color code then back to analog. That seems a little backwards but I could be wrong.

 

I'm using a GAL22V10 which is an older programmable logic chip. In the programming software I was able to set up a truth table of color code inputs and decoded outputs so hopefully you can do something similar with your code. It makes adjusting the color palette a breeze. Since you're going with a 24bit rgb color code you'll be able to directly port color palettes from jzintv which will be cool. Do you plan to have a program header so people can customize their palettes?

 

I had planed to bypass the AY-3-8915 entirely if possible is the only reason I asked.

 

I understand what you are doing now.

 

I haven't looked at the signal personally I just assume it has to be digital since it should only have two states on/off.

 

I haven't thought too far ahead on any board specifics. First I would be building the code; this would be my first foray into programming at all.

I do deff plan on having jumpers to toggle between RGB and component video. If able I'd have multiple pallets set with jumpers.

 

What I was assuming about the ext video input is that you can clock it at half the clock of RGB then OR those two together.

Say RGB is black 0000-0000 and ext video is white (on) then you end up with two signals 0000-0000 280ns and 1111-1111 140ns

when ORed I thought it should be just like the datasheet specifies.

 

You should be able to get away with 1 clock if you can specify length in the code somehow. Like if you trigger off the 280ns clock but only have that portion on for 140ns. Im really not sure if that's possible. Ill make my own thread sooner or later.

 

Here is a sample of my truth table. I don't want to paste the whole thing as it would take up alot of the screen.

I didnt put alot of time or thought into decimal to analog voltage value since its not specifically relevant to me besides testing.

 

V5,V4,V3,V2,V1

================================

red states

000 0000-0000

128 1000-0000

203 1100-1011

255 1111-1111

 

red for example can only be:

255 - 714mv

203 - 571mv

128 - 357mv

000 - ground

================================

green states

000 0000-0000

064 0100-0000

128 1000-0000

159 1001-1111

255 1111-1111

 

green for example can only be:

255 - 714mv

159 - 446mv

128 - 357mv

064 - 178.5mv

000 - ground

================================

blue states

000 0000-0000

101 0110-0101

128 1000-0000

255 1111-1111

 

blue for example can only be:

255 - 714mv

128 - 357mv

101 - 287mv

000 - ground

================================

Edited by the_crayon_king
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I wanted to try to give some kind of help with this and hopefully it makes some sense. First, I don't have an ECS myself, but based on what I can find online it doesn't seem to do any video generation itself. So, it should work with this mod or any others without any trouble.

 

The external video input pin on the cartridge port seems to have been used for two other things though. The first being the "Keyboard Component" and the second being the "System Changer".

 

From what I can find the external video input as used for the keyboard component, used genlocked video - meaning it was a composite video signal that was synchronized to the Color Processor Chip. If this is the case, there isn't a good solution to make it work.

 

The system changer also used composite video, but wasn't genlocked (so they also changed which pin on the cartridge port was used for external video). That's why the system changer only works with the Intellivision II, unless the Intellivision (all others) itself is modified. There is not a way to make this work without modifying the system changer. Since the system changer is just a 2600 that plugs into the Intellivision, with the Intellivision not really doing anything, it probably isn't worth trying to make it work.

Edited by hitokage
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I don't think so, it just switches to the external video source like a AV switchbox. Genlocked video could get switched seamlessly between internal and external composite video - like a video switcher used in a broadcast studio (the screen refresh is synchronized). Non-genlocked video, like used with the system changer, would cause some distortion when switching between the two signals - like a basic mechanical switchbox.

 

Here is a link to the Intellivision Wiki that describes how to modify an Intellivision (any non-Intellivision II) to use the system changer - http://wiki.intellivision.us/index.php?title=Intellivision_System_Changer_Support_Modification

 

This page is where I found the statement about the pin 8 of the cartridge port (external video) being genlocked (it's near the very bottom) - http://spatula-city.org/~im14u2c/intv/tech/master.html

Edited by hitokage
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To expand a bit more about what I said with the ECS working with any video mod - I think it works like a cartridge, with extra some hardware attached to it - like the Intellivoice. From what I understand of the ECS is that it doesn't have any built-in video chips, so any video/graphic type stuff is generated by the STIC, and doesn't use the external video pin.

 

The system changer on the other hand does have its own video generation chip and outputs a composite video signal, as it's almost a complete 2600, and that does use the external video pin.

 

To try to explain this better/clearer because sometimes I'm not very good explaining things - anything using the external video pin on the cartridge port (8 or 2) is sending composite video on that pin. The Intellivision just switches to it and doesn't do any processing on it at all.

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Thanks for the info hitokage. So the AY-3-8915 does convert an analog composite video signal to the 4bit digital color code? I wouldn't have guessed that.

The ay-3-8915 doesn't ouput the 4-bit digital colour code, it receives it as input from the STIC. The ay-3-8915 converts that digital code, which has a fifth bit for sync, blank, colour burst to a semi analog composite signal.
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  • 1 month later...

I had some time today to get at this project and got a finished installation. I'm working on assembly / installation instructions still but here are some pictures of the finished product. Once I get everything mailed out to the testers I will have to put this project on hold for a while, but I do plan to sell this mod once I get some other projects off my plate. I will post the plans to build it yourself at that time.

 

IMG_1131.thumb.JPG.c2897fa3f461c4346ff2d3615006caf9.JPG

 

IMG_1150.thumb.JPG.c7232f76c5aaa39bf5a82366349f277a.JPG

 

IMG_1151.thumb.JPG.44416d594df4a553a9bbb638cde47a2d.JPG

 

IMG_1152.thumb.JPG.c9620260dd7b580ade373c4168d3114a.JPG

 

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  • 4 months later...

Hi Emerson,

  I was wondering how your progress was coming on your RGB solution. As an OSSC user, I am very interested to see if your board will work with the OSSC (and when you will be willing to sell them). I also wanted to ask you if you planned on testing with RAD2X HDMI cables being released soon by Retro Gaming Cables. They are making one for the Genesis 2, so my thought was that this "should" work with your board. Let me know what you think

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23 hours ago, mattyv316 said:

Hi Emerson,

  I was wondering how your progress was coming on your RGB solution. As an OSSC user, I am very interested to see if your board will work with the OSSC (and when you will be willing to sell them). I also wanted to ask you if you planned on testing with RAD2X HDMI cables being released soon by Retro Gaming Cables. They are making one for the Genesis 2, so my thought was that this "should" work with your board. Let me know what you think

Hey thanks for asking!

 

Unfortunately my rgb mod did not perform very well. It does not work with the OSSC and in fact only seems to work reliably with either a modded crt or the cheap ebay rgb scaler. I haven't worked on the project since testing but I received some useful feedback for future improvements when I get around to it. I need to do more research before anything hits the market so no idea when it will be for sale.

 

I don't plan to test with the RAD2X HDMI cable.

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  • 7 months later...
  • 2 months later...
On 11/9/2019 at 1:36 PM, emerson said:

Hey thanks for asking!

 

Unfortunately my rgb mod did not perform very well. It does not work with the OSSC and in fact only seems to work reliably with either a modded crt or the cheap ebay rgb scaler. I haven't worked on the project since testing but I received some useful feedback for future improvements when I get around to it. I need to do more research before anything hits the market so no idea when it will be for sale.

 

I don't plan to test with the RAD2X HDMI cable.

I think I might have mentioned but I don't think the OSSC likes the resolution here. XRGB is a scaler OSSC is not right ?

 

Anyway I got my version of this mod to work:

https://i.imgur.com/pzosNlW.jpg

 

So maybe we can compare notes at some point.

If the only issue is this doesn't work with OSSC then I think you could produce what you have already.

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8 hours ago, the_crayon_king said:

I think I might have mentioned but I don't think the OSSC likes the resolution here. XRGB is a scaler OSSC is not right ?

 

Anyway I got my version of this mod to work:

https://i.imgur.com/pzosNlW.jpg

 

So maybe we can compare notes at some point.

If the only issue is this doesn't work with OSSC then I think you could produce what you have already.

There are several more issues with my mod than incompatibility with OSSC. It will certainly work for the homebrew arcade machine I designed it for, but I'd like to do better than that.

 

You say your mod works with the OSSC? Or better yet, how do you have your intellivision hooked up to the tv/monitor in your photo? It looks like there is some blurriness around the edges of characters, is that just the photo or is it your mod? Anyhow good work!

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47 minutes ago, emerson said:

There are several more issues with my mod than incompatibility with OSSC. It will certainly work for the homebrew arcade machine I designed it for, but I'd like to do better than that.

 

You say your mod works with the OSSC? Or better yet, how do you have your intellivision hooked up to the tv/monitor in your photo? It looks like there is some blurriness around the edges of characters, is that just the photo or is it your mod? Anyhow good work!

I don't have an OSSC but I assume if yours has an issue with the OSSC mine would as well. This is through an XRGB.

Something is wrong with my intelivision so I cannot confirm if the color bleeding is from the mod or the console itself.

If the blurriness is caused by the mod I would wager it is an issue with the clock.

 

The cool thing from here is that I can make these colors whatever I want and set them on jumpers. I haven't tried to put out YPbPr yet but I know that is possible as well.

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I believe the Intellivision RGB mod most folks have is missing some sync pulses (horizontal, I believe) which is believed to be the primary culprit when trying to use with the OSSC.  If yours is not missing those sync pulses it may function with an OSSC.  The issue with the OSSC is why most folks are looking for an alternative RGB mod for the Intellivisions.  The existing RGB mod works spectacularly with the Framemeister xRGB-mini.

 

I would be glad to build one of your designs to test with my OSSC.

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1 hour ago, KylJoy said:

I believe the Intellivision RGB mod most folks have is missing some sync pulses (horizontal, I believe) which is believed to be the primary culprit when trying to use with the OSSC.  If yours is not missing those sync pulses it may function with an OSSC.  The issue with the OSSC is why most folks are looking for an alternative RGB mod for the Intellivisions.  The existing RGB mod works spectacularly with the Framemeister xRGB-mini.

 

I would be glad to build one of your designs to test with my OSSC.

The code for sync should be :

1 X X 0 1 Sync

Which would mean

10001

10101

11001

11101

All can be sync. It is possible other mods may have overlooked that and just used 10001 or something idk.

 

I will compare my output sync to say the sync output from a LM1881 connected to the RF 1,2,4,8 area.

-----------------------------------------------------------------------------------------------------------

I have a few kinks I need to work out before this could be usable for somebody else. It is currently held together with hot glue and hope (which is also the title of my autobiography).

 

I'll make my own post since the kit I have should work on several different consoles only by modifying the code. I was just posting here since I assume Emerson and myself may share some relevant issues.

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  • 4 months later...

A little bump to this thread - since the OSSC compatibility didn't work out, at least for the moment.

 

There's been some great new converters/upscalers that I keep hearing good things about. RetroTink 2X SCART - 480p Upscaler for RGB SCART to HDMI. Has anyone here with an RGB modded Inty tried one yet? If so, is it compatible with the Intellivision?

 

I was thinking about taking the plunge, since I'm not really a fan of having to use the cheap Chinese upscaler that I currently have.  I'm hoping this'll be a excellent alternative, IF it's compatible. ;)

 

https://stoneagegamer.com/retrotink-2x-scart-480p-upscaler-for-rgb-scart-digital-video.html

Edited by SiLic0ne t0aD
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2 minutes ago, SiLic0ne t0aD said:

A little bump to this thread - since the OSSC compatibility didn't work out, at least for the moment.

 

There's been some great new converters/upscalers out that I keep hearing good things about. RetroTink 2X SCART - 480p Upscaler for RGB SCART. Has anyone here with an RGB modded Inty tried one? I was thinking about taking the plunge, since I'm not really a fan of having to use the cheap Chinese upscaler that I currently have.  I'm hoping this'll be a excellent alternative, IF it's compatible. ;)

 

https://stoneagegamer.com/retrotink-2x-scart-480p-upscaler-for-rgb-scart-digital-video.html

I have this setup and working....mostly. It looks great, but one annoying problem. When I use it with my LTO the video drops out while browsing through the game list on the LTO. I can get through the top part of the list, but If I try to scroll down....say 10 or 15 games, I have a hard time getting to a game. The screen will go black, I wait till it comes back up and scroll down a few more, and the screen will go black again.

Unfortunately, this is the best I can get. If I use other game carts, I have yet to see this issue.

Picture looks razor sharp though

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1 minute ago, mattyv316 said:

I have this setup and working....mostly. It looks great, but one annoying problem. When I use it with my LTO the video drops out while browsing through the game list on the LTO. I can get through the top part of the list, but If I try to scroll down....say 10 or 15 games, I have a hard time getting to a game. The screen will go black, I wait till it comes back up and scroll down a few more, and the screen will go black again.

Unfortunately, this is the best I can get. If I use other game carts, I have yet to see this issue.

Picture looks razor sharp though

Hey, that was quick! Thanks for the reply. :)

 

Do you have one of Fred's (juice) RGB mods installed in your Inty? That's what I have.

 

I think Emerson's RGB mod was somewhat similar, also not being compatible with the OSSC, unfortunately.

 

At least there's confirmation that the Retrotink does work, at least somewhat. Not sure what your issue could be though.. Maybe the it's your TV being "picky", but I'm no expert. I'm using a 43" Vizio d series from around 2018 and it's done well with everything I've thrown at it so far, so maybe I'll pick up one of these Retrotinks up and give it a shot after all. If it doesn't work out, I guess I have a backup for the OSSC and maybe my RGB modded N64 will look a little better. ?

 

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