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I think I have an elegant solution to the 7800 color thing. If you have a 7800 and an oscilloscope, please contact me.

PM sent.

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I think I have an elegant solution to the 7800 color thing. If you have a 7800 and an oscilloscope, please contact me.

I am also interested, can you publish the solution if it works?

Olix

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I am also interested, can you publish the solution if it works?

Olix

Here's what we've got:

TIA color has 2 states: Pull-down and open.

Maria color has 3 states: Pull-up, pull-down, and open.

When TIA is dormant/open (7800 game), it is simply pulled up by the 1K resistor. This means our combination point has a 5.7K pull-up (adding the two resistors).

When Maria is dormant/open (2600 game), no current flows through the 4.3K resistor.

The combination point is always pulled down through a 470 ohm resistor. We'll just look at DC and ignore the impact of the LC output circuit.

During a 2600 game:

when TIA color is high (not driven) the combination point is 0.38V. (470/(5700+470))*5

when TIA color is driven low, the combination point is 0V because all the current from the 1K pull-up flows into TIA.

Maria's color pin is floating, so the voltage on it will be the same as at the combination point.

During a 7800 game:

A 5.7K path to 5V is always present. When Maria color is driven high this is paralled with a 4.3K path to 5V, so we get an effective path of 2.534K. The voltage becomes 0.78V (470/2534)*5

When Maria color is driven low, we can combine the 4.3K with the 470 for a parallel resistance of 424 ohms. This yields 0.35V. (424/6124)*5

So, the chroma signals are close in amplitude (0.38V vs 0.43V) even though one has a DC offset (until it reaches the cap).

In 2600 mode, Maria's pin will always read as a logic 0 because TIA won't drive it higher than 0.38V.

In 7800 mode, TIA's pin will always read high because of the local 1K pull-up.

In order to combine a normally high and a normally low signal, you need to invert one, or use an exclusive-OR (XOR) gate.

Getting back to UAV...

UAV uses an XOR gate to provide the artifact inversion feature. If you put Maria Color into the normal color input and connect TIA Color to the invert pin in the configuration header, you should get both color signals combined.

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Given that TIA is used in 7800 mode, are the registers (esp colours) cleared on powerup by the Bios?

Fairly sure they can be in indeterminate states.

Do you use some method to determine which signal should be used?

I have a 'scope and a 7800 though can't really participate. A few years ago I swapped a spare 7800 for working 1084 to replace my dead one... and my only 7800 wall-wart went as well.

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I don't know enough about 7800 programming to know if video from the TIA is completely suppressed, but I know that if the TIA produces even a colorburst, it will interfere with Maria's video.

In 7800 mode, you are restricted to the first 32 TIA registers but I don't know much more about it. I would imagine that TIA is kept in VBLANK mode to hold the state steady. Because OR gates are used, it appears that TIAs outputs are stuck low in 7800 mode, which is wonderful.

Anyway, someone's looking into it so I can give solid advice here.

I'm using this schematic:

http://atariage.com/7800/archives/schematics_ntsc/Schematic_7800_NTSC_Low.html

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I had a look through the 7800 Bios "source" but not a lot of help. There is a clear TIA loop after label "SETMARIA" that clears only addresses 01-2C.

But I can find no reference to setting the VBLANK control (\$01) or VSYNC (\$00) - in both cases zero values do nothing. Value 2 would need to be written to hold VSYNC. A "sensible" setup to me would have VSYNC=00 and VBLANK=02.

In normal 7800 operation the only needed TIA addresses should be \$01 (write to VBLANK high bits for setting up pots), \$15-\$1A (writes for audio) and \$08-\$0D (input read bits)

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I'll post a question in the 7800 forum.

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Hi Bryan, this UAV is veery good invention...
if it's still possible
i'm interested in ONE pcs custom board (complete-kit: basic board and non-soldered but included all the parts)
for 800xl, pal
deliv. to Poland
(btw, paypal will be acceptable payment's method?)
regards,
t27

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Hi Bryan, PM sent!

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I put in an earlier comment requesting 1-3, but didn't follow up with a later answer once there was a more concrete solicitation. I'll try to follow this to see if you open up the run. I'd like 2, one for a 1200XL and one for an 800XL - depending on price, which I haven't seen a rough estimate of yet. Am I overlooking this? Thank you.

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So on the Atari 8 bits do we continue using the built in monitor ports or do we have to wire in new ports? What about the 600XL, can this be installed in that? (US models don't have the monitor port)

Edited by tjlazer

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So on the Atari 8 bits do we continue using the built in monitor ports or do we have to wire in new ports? What about the 600XL, can this be installed in that? (US models don't have the monitor port)

You can disconnect the internal signals and wire to the existing DIN port, or you can wire in whatever ports you want or runs cables out of the case.

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So on the Atari 8 bits do we continue using the built in monitor ports or do we have to wire in new ports? What about the 600XL, can this be installed in that? (US models don't have the monitor port)

This is pretty easy for the 600xl. Under the channel selector switch are the solder holes for a regular video jack. This is true for all US 600xl models I've seen. Solder a new jack in place, and connect Bryan's board. There will be some minor clearance issues that will be addressed in the docs, but compared to all other alternatives that I've seen, this is very easy and the results are amazing. You will have to cut a hole for the monitor plug. Look here at AA or the web for the Sumrall Atari video mod or 600xl video mods. Of course, you still have 16kb, so that needs to be addressed unless basically using it as a cartridge game machine.

- Larry

Edit: Read a post this AM that indicated some early 600XL's don't have the solder holes on the mobo. That certainly would not be a show-stopper, but you would need to mount the video jack differently.

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The key is of course if you use the built in monitor port to disable the on board video to the jack or you will get interference.

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This is a message for everyone messaging me for boards at this point:

I am assembling these by hand and I cannot promise anything past the 130 board limit, but I will keep everyone's info and let you know if I'm able to fill extra orders.

Also, the board will be available in the AtariAge store soon.

To everyone who has placed an order:

Next week I will be posting our (Larry, orpheuswaking, and myself) findings on which version of the board to install in various machines. I will make all adjustments to the list at that time.

Thanks!

-Bry

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I'm soon going to make a more-or-less permanent installation in a new 600XL. Do you believe that it will make any difference if I use a shielded cable for the connecting wires, and connect the shield to the ground band in the XL? The test results were excellent with no shielding, but maybe "an ounce of prevention?" Anyway, it will make for a neater installation, I think.

-Larry

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This is pretty easy for the 600xl. Under the channel selector switch are the solder holes for a regular video jack. This is true for all US 600xl models I've seen. Solder a new jack in place, and connect Bryan's board. There will be some minor clearance issues that will be addressed in the docs, but compared to all other alternatives that I've seen, this is very easy and the results are amazing. You will have to cut a hole for the monitor plug. Look here at AA or the web for the Sumrall Atari video mod or 600xl video mods. Of course, you still have 16kb, so that needs to be addressed unless basically using it as a cartridge game machine.

Does the RF modulator need to be removed to make room for the video jack?

I already did the 64k RAM hack

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Does the RF modulator need to be removed to make room for the video jack?

I already did the 64k RAM hack

No, you should not have to do that. But open your 600XL and look at the channel selector area of the mobo. The video jack is a bit less than 7/8" wide (max), and sits right next to the RF modulator. You already have 64K -- great! The UAV will make you a really nice XL.

The Ram 320XL makes a nice upgrade, too, but when you attach it, then you lose the PBI. Hopefully, Ctirad will be able to complete the Ram 320/576 XL that will have a PBI pass-through.

I have a very nice 600XL with the 512K SRAM upgrade in it + a 32-in-1 OS + really good S-Video. I use it quite a bit.

-Larry

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7800 update...

I verified that TIA keeps the COL pin high during VSYNC but not VBLANK. So, the 7800 must keep TIA in VSYNC mode. It's the only way to silence it as far as I can tell (no one ever answered that question in the 7800 forum, so I guess no one knows).

Anyway, the easy way to combine Maria and TIA is to connect Maria's color into the normal terminal spot, and connect TIA's color to the jumper area as shown.

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I'd like 4-full and 1 without pins/jacks.

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I was able to try UAV with a Samsung CRT TV. No surprises. Not quite as sharp as my JVC monitor, but really nice.

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By the way, speaking of the 7800 is there a decent solution for getting stereo audio? Something that mixes TIA 1 to left, TIA 2 to right, and the cartridge audio to the center?

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Let us know when we should watch our inboxes here.

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I've updated the installation post. Let me know what changes you wish to make. I'm now making it available as:

1. Plug-In board. Easiest option, but doesn't fit everywhere. \$20

2. Basic board. A little more soldering, but can be installed in anything. \$17

3. Basic board kit. You get a Basic board, plus the parts to make it into a Plug-In board (socket pins, configuration header and jumpers, output screw terminal block). This way you can add just the extra parts that fit. \$20.

The Plug-In board and Basic board kit also come with a 16-pin socket.

There is no difference in video quality, just the pins and connectors.

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I've updated the installation post. Let me know what changes you wish to make. I'm now making it available as:

1. Plug-In board. Easiest option, but doesn't fit everywhere. \$20

2. Basic board. A little more soldering, but can be installed in anything. \$17

3. Basic board kit. You get a Basic board, plus the parts to make it into a Plug-In board (socket pins, configuration header and jumpers, output screw terminal block). This way you can add just the extra parts that fit. \$20.

The Plug-In board and Basic board kit also come with a 16-pin socket.

There is no difference in video quality, just the pins and connectors.

Looks fantastic, Bryan. Very much looking forward to these!

One quick question, and if this was discussed earlier in the giant thread I apologize: will there be close-up installation pics and/or an illustrated installation guide posted somewhere for each of the different models/options? For instance, I plan to put one in my daily-driver 800XL which has a socketed 4050, and another in a 4-switch Woody 2600, without the chip. Your "preview" pics linked in the installation post are not very large, for instance, and don't have pins listed for the various solder points.

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