Fairchild Channel F RGB notes

[the_crayon_king]

4 hours ago, e5frog said:

Nice work!
Is gate delays in the vicinity of what is needed? (usually in the range of 6-33ns)

 

If color information goes into the RAM it should be possible to pick it up earlier? 

 

When setting the color information in the software you set the color on port 1, column on port 4 and row on port 5.
Color codes:

green    = $00 (%00000000)
red    = $40 (%01000000)
blue    = $80 (%10000000)
bkg    = $C0 (%11000000)

I believe anything sent through the ports is inverted, you invert it before writing it to the port.

Activation sequence for setting VRAM with this information is done with:
$60 on port 0 (port 0 is on CPU pins 16,11,10,5,36,31,30,29 bit0-7)

$40  to port 0 (keeps the bit 1 on joystick signals, zeroes - on the input of the port - the other bits)
Then a delay is needed for the real machine (not in MESS emulation) before you try and change graphics again or there's garbage. 

So when there's a pulse on bit 5 (pin 31) of port 0, reading the data from ports 1, 4 and 5 at that pulse gives the color and coordinate. 
You'd need a video memory to plot in and then an output routine for the RGB/HDMI/whatever to draw these. 

 

Not sure how you do it, perhaps decoding the actual analog TV output is a better/easier and cheaper approach.

Perhaps also an easier DIY method. 
 

 

 

 

 

 

Well poking around made my RF stop working. Probably something to do with the connection to RF since I still see all the signals over composite.

Composite looks noisy as heck. I am not sure what they are doing but it appears like the have the burst clock going all the time over blank, white, black, grey, sync etc.

I am no expert but I am pretty sure there shouldn't be any chrominance/burst during any of those colors/conditions. Blank should have burst after sync and then the color besides the ones listed above should be clocked to that but I am seeing it constantly.

I think the RF carrier wave is either already applied or something. That should be removed along with the audio to make composite. The repeating signal I am seeing is 48ns from one pulse to the next. So if I can poke around a little more and find a 48ns signal connected to the output then it is likely removing that would "fix" the video.

So I will attempt to do that. This will just be something I use to look at video besides the RGB I am attempting to create so I can verify the colors.

 

 

 

Anyway, I can't redraw the locations of things only delay them. That would be a limit to the CPLD I am using and my lack of knowledge of how to do such a thing.

The only thing I can do is draw things from left to right top to bottom. I will work this delay thing and see what comes of it.

 

Edit:

So for composite you just need to solder to that spot and lift that pin. Then amp the signal 4x (12db gain). You can do this sending the signal through a 7314/7316 twice (which is what I did). The noise that I saw is probably just a case of breadboarditus. I will make a proper circuit for this at some point but I think you get the idea. As for S-video I am too afraid to keep poking around on this board directly but the same thing probably applies.

 

The better way would be to use an op amp/transistor to amp by Y/C by 6db and then a FMS640X to get S-Video and Composite. The first op-amp/transistor being possibly useful for additional filtering. I will actually have to lift those areas and measure the voltage but I would wager that is the case. I can make a board for this if someone is willing to order/try it. I am just using the CV that I have made for bare bones stuff whilst I try to figure out RGB.

 

 

 

Edited February 3, 2021 by the_crayon_king

[+KylJoy]

Hey, I've been lurking in here and already installed your "Baked Potato" board in an Intellivision and in an Emerson Arcadia 2001 with great success.  I would LOVE to get RGB out of my Fairchild Channel F.  I'm selfishly hoping you've made more progress here.  I have model I and II units that I could try with.  Do you think the "Baked Potato" or "Orange Peel" RGB boards can work with the Channel F?

[the_crayon_king]

@KylJoy the problem is no matter how careful I am my fairchilds keep breaking. I have three and they were very expensive. 

Where I was tapping was/is a non-starter. I was trying to brute force a solution. I thought it would be easy since there are so few colors. 

I was tapping solely Luma pins; Yet the data needed for real RGB is obfuscated in RAM.

 

I am guessing there is a color register that is setup by the PPU receiving certain bits? 

Really what I need is a truth table then a board would be easy to design.