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Still working on GTIA V-Gate?


olix

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More changes...

 

UGV_V1.1_PCB.thumb.png.de094558f14e3c0852a78e42c48d44b4.png

 

Still the same board size, but I've changed the design - adding a 'True Black' level creation circuit. In order to cram all of this into the same footprint, I had to give up the separate V-Gate enable header. V-gate will be controlled through pin 3 and 4 of the ICSP header instead. It's kinda of imperative that I don't increase the board size in order to have it fit the widest number of Atari 8-bit computers.

 

I also updated the name to be Ultimate Gated Video or UGV. I really felt this was needed since this is much more than a V-Gate board.

 

So what's a 'True Black' level?

 

In standard composite video there is a 50mv step that occurs shortly after the HSYNC pulse, and then drops back down to the normal blanking level just prior to the next SYNC pulse. This also happens in the luma signal of S-Video. This 50mv step up equals the black level, and as the name denotes lets the monitor know what is suppose to be the blackest black.

 

DI39Fig05.gif

 

 

The Atari, just like many other computers of the era kinda cheated on this, and made the blanking level the same as black

(Notice there is no step up in voltage level following the Line Synchronization pulse).

 

Atari_Video_Waveform.png.40f169f7daf0af54e295f28c3d472f59.png

 

Now for the most part this still works on most monitors either of the era (CRTs) or on the newer LCDs. However many of the cheaper HDMI converters don't properly decode the combined blanking/black level and the end result ends up being very high contrast/over saturated video. So I added some additional circuitry to recreate 'True Black' independent of the blanking signal.

 

More info about how this was achieved will be forthcoming.

 

Edited by mytek
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  • 4 weeks later...

Yet more changes...

 

I stuffed one of the sample boards with parts and began testing a few days ago, wherein I started to notice a problem with the automatic black level restoration circuit. Try as I might, I just couldn't get it to work as good as I thought it should. So push came to shove and I decided to go manual instead. This of course required a new PCB layout (see below).

 

UGV_V1.3_PCB_assignments.thumb.png.7ac58110bfe48ade66c61108fbe23f60.png

 

The dip switch (SW1) allows for selecting the 4 different black levels in order to accommodate differing requirements dependent upon the monitor or video converter in use. With both switches set to OFF the video output characteristics are very similar to a UAV in quality, contrast, brightness, and color. By activating the dip switches, 3 additional black levels are available, with each one at a higher point than the standard video. One switch is a fine adjustment, and the other is a course adjustment. Essentially what is happening is that the sync and the white level remain the same in all switch positions, but the top of sync which is also the black level can be raised, thereby decreasing the overall amplitude of the video data. This allows the cheaper HDMI video converters to not be over saturated and/or too contrasty.

 

I've also designed a mating mini-DIN-4 (S-Video) connector PCB for those times when you would rather have a standard S-Video connection. The idea is to allow the normal Atari 5 pin DIN to supply the audio and composite video with the UGV's composite signal preferably being routed in place of the stock Atari one, heading out of the 5 pin DIN A/V jack.

 

S-Video Connector Interface Board (only top side traces are shown)

UGV_INTFC.png.5bc0a2eef0b49dc5431542c95346a344.png

 

When using this connector board it is suggested that the RF modulator be removed, and then use the RF out hole for accessing the S-Video jack. Standoffs would then be used to mount the board at the correct height above the Atari motherboard. Those metal 4-40 standoffs (jack Screws) that come with Dsub connectors would be perfect, and also tie the Mini-DIN's case to the shield ground on the Atari motherboard.

 

JackScrew.png.15df3bab57f64b716fa5cd9ea4c7f9a2.png

 

With these two boards and some jumper wires, a solder-less installation is quite possible. Well assuming you don't care about replacing the stock composite signal with the one from the UGV. And before someone starts suggesting that an RCA jack be included on this interface board for the composite signal, I already played around with that idea and unfortunately it wouldn't fly with how the RF output hole varies significantly between an XL and XE - depending upon which one you designed for, it wouldn't fit in the other due to available space. Personally if I have a choice between S-Video and composite, I'd choose S-Video every single time. Besides artifacted colors only work on NTSC systems, and even at that it looks kinda crappy in my opinion.

 

1951-01.jpg

 

I'll be ordering some more sample boards soon ;-)

 

Edited by mytek
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3 hours ago, olix said:

Glad to hear the project is making progress.

Could you please post the current schematic here.

It is very interesting and i can learn a lot from watching the changes in the circuit.

I'll be holding off on posting the schematic until I've assembled the new V1.3 version and confirmed the component values that work best in this new design. Probably be around 2 weeks from now.

 

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  • 4 weeks later...

UGV Ultimate Gated Video Board - Released Today

 

UGV_PCB_Overview.thumb.JPG.381dc7947c8a52875e704cedaaca1845.JPG

 

LINK: https://ataribits.weebly.com/ugv.html

 

I still have some work to do on a demo video that'll get posted on that page eventually, but I just couldn't hold off any longer on giving you guys a glimpse of the completed project :)

 

This board takes the place of the previous V-Gate only GTIA piggyback board that was put on indefinite hold many years ago, but now sports it's own high quality analog video output driver. It took some meddling through various projects to really get the V-gate technology into a form that I truly liked, and that is thanks in large part to the 576NUC+ project. However the global supply shortages have made the PIC chips near impossible to find now days, but luckily I was also able to secure a good source for the PIC12F1572 chips that the UGV requires via AliExpress (there is a link on my website). I purchased 10 of those, and have thus far used 5 of them in my experiments with no issues.

 

I still consider this board to be DIY, although it will require excellent soldering skills on the part of the assembler due to the small nature of the components. I used the largest SMD package style (SOIC) for all the ICs, and went with THT for the resistors and capacitors, and everything else. Sticking with THT on resistors and capacitors kept the number of vias and crossed signal paths to a minimum which is very important on an analog video board. If I had used SMD devices for this aspect, any size reduction would have required very tiny fiddly packages, and made the PCB layout very difficult because of being limited to one trace layer (a lot more vias would have been needed).

 

the FMS6400 video driver chip is obsolete. However they are easily sourced from eBay, and I have yet to get a bad batch through that avenue. Since these are not considered a popular item like an EEPROM for your car or a Pokey chip for your Atari, there appears to be less appeal to sell fakes of these.

 

Although I haven't checked on the real hardware to be sure, I think the UGV should also work in a 400 or 800 as well.

 

And I'd like to acknowledge @olix for starting this topic that put the fire under my butt to bring this project into reality ;)

 

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2 hours ago, olix said:

Great news! PCBs are ordered and I can't wait for my boards to arrive. Most of the components are already in my parts box.

Cool ?

 

This will probably not be an issue for you since you will most likely be installing yours in a PAL system, but if it's NTSC there is most likely a jumper that needs to be either cut or removed on the motherboard. Failure to do so will result in a blue vertical line on the screen left, and a red one on the screen right.

 

For some unknown to me reason, Atari was jumpering the GTIA OSC pin 28 to the PAL pin 16 on the NTSC boards (currently I don't know if this is all NTSC systems). An NTSC GTIA's pin 16 is a 'no connect' inside the chip, and is only used on the PAL GTIA's for insertion of the color burst clock. My only way to detect if V-Gate is in a PAL or NTSC system is via GTIA pin 16 (I look for clocking). So if that pin is tied to the OSC pin 28 then the V-Gate chip thinks it's in a PAL system even if it's not.

 

So for a 600 or 800XL the jumper is labeled W2 on the silkscreen and is directly next to the crystal oscillator circuit. On a 1200XL it's labeled as W10 to the right of the GTIA chip, but I've yet to see a 1200XL with this jumper installed, so that shows you it was unimportant since all 1200XLs were NTSC.

 

I'll have to figure out if this jumper exists on the XEs or the original 400/800 systems.

 

Bottom line is, there is no good reason to have this jumper in place, and nothing bad will happen with it removed. All of my custom motherboards (1088XEL/XLD, and 576NUC+) do not do this.

 

If anyone has a good explanation of why this jumper exists, I'd love to hear it :)

 

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32 minutes ago, mytek said:

I'll have to figure out if this jumper exists on the XEs or the original 400/800 systems.

Going by the schematic in the Sams Computer Facts for the 130XE GTIA pin 16 appears to connect to the U21/Q6 circuit(for European/PAL models)driven by the oscillator, or to the oscillator via jumper W2.

 

1911897028_130XEGTIAoscillatorconnection.png.91bf7c354f4f67698f67ff8c6035ff90.png

Edited by BillC
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Ok here's what I've got thus far. On all XLs (bedsides the 1200) and all XEs the jumper that needs to be cut or removed is labeled W2.

 

Here's some pics for location purposes.

 

600XL

Atari_600XL_W2.thumb.png.64e211cec73a91ebbd6602aef3cbb593.png

 

800XL

Atari_800XL_W2.thumb.png.562c00d3412ac840a61563a06e4b4ff4.png

 

65XE

Atari_65XE_W2.thumb.png.72f30c5f9bf32cd81a61456b66be32a0.png

 

130XE

Atari_130XE_W2.thumb.png.8649335a2445336dbd7eb1bcd7935a97.png

 

XEGS

Atari_XEGS_W2.thumb.png.4c9ebd1519f743dd2a6c96b3831f6408.png

 

And here's the 1200XL's equivalent labeled as W10, although I've never seen it installed.

1200XL

Atari_1200XL_W10.thumb.png.80f2abca656db89543d116495c42b666.png

 

The fact that the 1200XL never used it, is a pretty good clue that it was never needed in the first place.

 

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13 hours ago, mytek said:

...

 

I still consider this board to be DIY, although it will require excellent soldering skills on the part of the assembler due to the small nature of the components. I used the largest SMD package style (SOIC) for all the ICs, and went with THT for the resistors and capacitors, and everything else. Sticking with THT on resistors and capacitors kept the number of vias and crossed signal paths to a minimum which is very important on an analog video board. If I had used SMD devices for this aspect, any size reduction would have required very tiny fiddly packages, and made the PCB layout very difficult because of being limited to one trace layer (a lot more vias would have been needed).

 

...

 

In fact, the assembly with the SMD components will be a small challenge for me.

But that's what makes it so much fun.

So thank you very much for releasing this project as DIY.
Your hardware developments are always a great enrichment for the whole Atari fan base.

 

This is only the second project I've assembled using SMD components.

The first was Panos' new XE board with an integrated UAV. Everything worked fine, so I'll get the V-gate right too.

 

My very first SMD soldering work:

SMD-Bauteile.jpg

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7 hours ago, mytek said:

Ok here's what I've got thus far. On all XLs (bedsides the 1200) and all XEs the jumper that needs to be cut or removed is labeled W2.

 

 

The fact that the 1200XL never used it, is a pretty good clue that it was never needed in the first place.

 

Be careful. On PAL machines, this delivers the color carrier through a second crystal, which is 5/4th of the NTSC carrier, I wouldn't really cut it there.

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17 minutes ago, thorfdbg said:

Be careful. On PAL machines, this delivers the color carrier through a second crystal, which is 5/4th of the NTSC carrier, I wouldn't really cut it there.

The discussion is about the need to remove it on NTSC machines, otherwise the V-Gate circuit will detect the video system as PAL.

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6 hours ago, thorfdbg said:

Be careful. On PAL machines, this delivers the color carrier through a second crystal, which is 5/4th of the NTSC carrier, I wouldn't really cut it there.

Yes as @BillC stated no modifications are being suggested for PAL machines. The recommendation for cutting or removal of the W2 jumper is only referencing NTSC machines.

 

However unless things are different in regards to either the 800XL or 130XE, I think you are mistaken on W2 being needed in a PAL machine. In fact it would actually be a very bad mistake to leave it in place for a PAL system, since it would short the output of the Color Burst Oscillator to the output of the Primary Oscillator.

 

Schematic: Atari 130XE W2 Jumper Detail

 

130XE_W2.thumb.png.d7781413fa8d78107d9f220ea22face2.png

 

 

Schematic: Atari 800XL W2 Jumper Detail

 

800XL_W2.thumb.png.4627b1e2d6377d7e00979712c6b5ca0b.png

 

 

From what I know via my own experience, the absence of W2 on any PAL machine is a non issue, but its presence would be detrimental to the operation of said machine. As for NTSC machines, they too can have this jumper absence with no ill effects to their operation. An NTSC GTIA chip's pin 16 is designated as a 'no connect' pin. My proof for the non-requirement of W2 (or W10 in a 1200XL) in an NTSC machine is the 1200XLs non-use, and the complete absence in a 1088XEL, 1088XLD, or 576NUC+, all of which work just fine without it.

:)

Edited by mytek
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Getting back to the NTSC GTIA P/N: C014805...

 

I checked the original Atari 400/800 service manual and the SAMs photo-facts for the same machines. They all show the NTSC GTIA pin 16 as a 'no connect' on the schematic, and when checking the CPU PCB card (where GTIA and Antic share the space)  there is indeed nothing connected to pin 16. This also holds true for the original release with the CTIA chip.

 

Bottom line as to why Atari felt compelled to jumper the OSC output to pin 16 on the NTSC GTIA which is a 'no connect' on later machines is beyond my level to comprehend :?

 

The only possibility I can think of is that after the 400/800 they started thinking of maybe making a new dual purpose (NTSC/PAL) chip to take its place. So if it saw 3.58 Mhz clocking on pin 16 it would shift gears and become an NTSC version, and if it saw 4.43 Mhz instead it would become a PAL version. Of course if that was the thinking BITD it never materialized, and really doesn't matter at this point in time.

 

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I just mocked this up since I don't have either a 400 or 800 in my collection.

 

Atari 400/800 Sally CPU Board with UGV (NTSC Version Shown)

UGV_400-800.thumb.png.d8042f0597d2fe946d17781d8dcdf4cd.png

 

It looks like the UGV board will fit, although the ICSP pins might interfere with the edge card socket, so it might require a different plan for that header. Could just leave it out, and do a temporary 'pogo-pin' connect to flash the PIC chip.

 

As for depth, the UGV was made to require very little headroom through a low profile design, so there's a good chance it'll fit the available space. Equivalent to adding one stacked socket.

 

Edited by mytek
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10 minutes ago, mytek said:

I just mocked this up since I don't have either a 400 or 800 in my collection.

 

Atari 400/800 Sally CPU Board with UGV (NTSC Version Shown)

UGV_400-800.thumb.png.d8042f0597d2fe946d17781d8dcdf4cd.png

 

It looks like the UGV board will fit, although the ICSP pins might interfere with the edge card socket, so it might require a different plan for that header. Could just leave it out, and do a temporary 'pogo-pin' connect to flash the PIC chip.

 

As for depth, the UGV was made to require very little headroom through a low profile design, so there's a good chance it'll fit the available space. Equivalent to adding one stacked socket.

 

I'm interested in several of these boards.  When I get them, I can try fitting it to my 800 (it's still taken apart).

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Apologies if this is a silly question, but does this  *eliminate* the colored borders from the signal, or does it turn the borders black?

 

In other words, if I used this device on a CRT or upscaler, would it allow the image to fill more of the screen without requiring me to crop the borders?

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7 hours ago, Stephen said:

I'm interested in several of these boards.  When I get them, I can try fitting it to my 800 (it's still taken apart).

Board files are available from my website right now :)

 

3 hours ago, DragonFire said:

Apologies if this is a silly question, but does this  *eliminate* the colored borders from the signal, or does it turn the borders black?

Well first of all it does not alter the borders generated by the Atari itself. However if those borders extend into what would be over scan territory on a CRT, UGV blanks that information and turns it black.

 

Here's a video showing the over scan information being eliminated on a Vizio LCD monitor.

 

 

BTW, I don't know if people who have Sophias realize it, but those video boards also have a V-Gate function built-in.

 

3 hours ago, DragonFire said:

In other words, if I used this device on a CRT or upscaler, would it allow the image to fill more of the screen without requiring me to crop the borders?

Not sure how to answer that, other than there is no more video data being added.

 

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I just realized that the CPU board image I used for my 400/800 mock-up was not a Sally version, but the original standard 6502 version with the individual tri-state buffers. I'll have to see if I have a good image of the later Sally board for comparison.

 

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37 minutes ago, olix said:

I'm still missing the Schottky SD103 diode. But I still have a lot of the BAT-48 (also a 40V Schottky). Can I use this instead of the SD103?

Yep that one works just fine and is in the same package size as the SD103. I started spec'ing the SD103 when I could no longer get BAT-48's.

 

Also I just discovered that Digi-Key no longer has any stock of the 10uf ceramic capacitor P/N: C322C106K3R5TA But Mouser does as part number: 80-C322C106K3R.

 

This is why I also list the manufacturer number as well as the Digi-Key number on the BOM. Darn supply shortages :mad:

 

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2 hours ago, Panther said:

Very nicely organized!

Thanks :)

 

If you look at the bottom right on that webpage you'll see that I've reserved space for a demo video to come. I did do a very quick and somewhat rushed one which I already posted earlier to this topic. I literally grabbed the GoPro 15 minutes before I needed to leave and did a non-scripted demo. I really need to take the time to do it right and cover all the bases. But at least on that first video you can get an idea of the video quality and the V-gate in operation.

 

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I've all the components on hand, so I'll just have to order some PCBs and try out a couple of these.  I can finally dispose of these original version V-Gate PCBs I have but never used.  I haven't used CRTs in ages, so this is a very useful addition.

 

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