SEGA Genesis 1 ext port pinout question and other video/audio comments

[HDTV1080P]

I have owned a Pioneer Laseractive system from the mid 90’s which has native composite video and stereo audio using the built in native factory installed RCA jacks. The Laseractive system plays Sega Genesis cartridges, CD-ROM’s, and exclusive 12 inch Sega Laserdisc games. This 1993 Laseractive 16 bit videogame system was a big improvement when compared to the 1982 ColecoVision and 1983 ADAM computer that I used exclusive for game playing for 10 years.

 

I was reading online that the original Sega Genesis 1 with High Definition Graphics has a exclusive ext port. Does anyone have a link with the pin out information for the ext port? Perhaps this is just a DB-9 serial communication port at 2400 or 19200 baud. Or perhaps the ext port has video and stereo audio output on a few of the pins. A pin out schematic of this ext port would be ideal.

 

I was surprised to hear that the 8 pin DIN jack on the Sega Genesis only outputs mono audio with the left and right channels combined. To get true stereo sound from the Sega Genesis one has to use the headphone jack with either headphones or a headphone to RCA adapter plug. The Sega Genesis was Sega’s very first videogame system with native stereo sound.

 

There appears to be a wide selection of 5 pin DIN plugs with composite video for the Genesis 1, however the Genesis 1 also offers native RGB output and its hard to find a USA dealer that offers a 8 pin DIN plug with RGB output cable or component video output cable. I see online there is a internal S-Video conversion circuit for the Genesis, however if the system is offering true RGB output that is a better option. One should be able to make a RGB cable for a old computer monitor or a component video cable that works with the Genesis. Now internally modifying the Genesis to have native HDMI output would be ideal.

 

There are new Sega Genesis clones that have the exact same look as the original Genesis plus the added benefit of having a HDMI output.

Edited October 26, 2018 by HDTV1080P

[HDTV1080P]

One of the awesome features of the original 16 bit Sega Genesis 1 is that its backwards compatible with the old 8 bit Sega Master System games if one owns the Power Base Converter adapter.

 

This is the only 16 bit videogame system that I know of that is backwards compatible with its older classic 8 bit videogames.

Edited October 26, 2018 by HDTV1080P

[HDTV1080P]

It is interesting that the Sega Genesis System Console model number 1601 label on the bottom of the case mentions that it needs a 9 volt DC adapter at 1.2amps, however the Sega 1602-1 power supply is 10 volt DC at 1.2 amps. I know the extra 1 volt is a minor issue, however that is looking like Sega made a misprint on voltage rating. Most likely any DC power adapter that is 9 volts or 10 volts DC well work as long as it can output 1.2 amps (plus the plug needs to be the right polarity and size).

Edited October 26, 2018 by HDTV1080P

[+-^CrossBow^-]

Nothing from it other than being a serial output port for using the Mega Modem at 2400 baud. That is why it was later removed as it was never used here in the states. There ins't any video or audio lines from it by default. However, since it was never used here in the states, you could if you wanted... cut the traces off the board that connect to the pins except the ground as you can leave that in place. And then fashion yourself a cable that has the RCA and s-video jacks etc from it as a break out cable of sorts. In other words you reuse that port to provide additional connections the Genesis model 1 doesn't have on its own currently.

 

And just so you are aware, the model 1s tend to exhibit nasty jail bars on the s-video and even RGB signals. Further modification is usually required to try and minimize that as much as possible.

[+chicgamer]

This Sega-16 thread response by TmEE may answer your EXT port question.

 

Retro Access sells RGB SCART cables for the Genesis model 1.

 

For component, you can get the HD Retrovision Genesis 2 cables with an adapter.

Edited October 26, 2018 by chicgamer

[+-^CrossBow^-]

What Chicgamer said above...

 

Also a new company I'm quite impressed with also makes good SCART RGB cables for the Genesis systems.

 

https://insurrectionindustries.com/product/

 

They are in the US so quick to ship and slightly cheaper than ordering from overseas.

[HDTV1080P]

All my displays are USA or North American models and the SCART connection was designed for mainly the Europen market. I would need to get some type of adapter to use the SCART interface in the United States. This is why I would rather have a RGB connector that would either connect to a USA RGB computer monitor or a component video cable that connects to several millions of old home theater tube TV’s, projectors and flat panels. However many new displays have dropped component video and RGB and have went 100% HDMI.

 

Thanks everyone for the useful information. The DB-9 serial port is only a communication port for data, I was hoping that it offered native stereo sound, but since it does not one needs to use the headphone jack to get stereo sound out of the original Genesis one model.

 

That company that is only offering a 9 pin DIN component video cable for the Genesis 2 model, I am guessing that model was more popular, at least they sale an adapter that connects the component video cable to the Genesis one and Master System models. There must not be enough demand to make a component video cable with a dedicated 8 pin DIN connector and instead both the Neo Geo and Genesis One need a conversion adapter cable to use the component video cable that was designed for the Sega Genesis 2.

 

The side expansion port on the Sega Genesis system is nice and large expansion interface just like on my old 8 bit 1982 ColecoVision and 1983 ADAM computer. I see SEGA came out with a lot of interesting expansion modules that either use the top cartridge slot or side expansion. However no 16 bit SEGA computer system was every developed since they were not interested in making a home computer system.

 

I wonder if any third party company has thought about using the side expansion slot on the Sega Genesis. Perhaps that expansion slot offers RGB video and stereo output along with power input to power the game system (I have not looked at the pinout of the expansion slot). However my point is instead of internally modifying the Sega Genesis one console, perhaps a third party hardware device could plug in the side expansion port to offer native HDMI output with a new graphics processor that would be compatible with existing games. The Sega CD uses the side expansion slot, however with some type of y adapter made both the SEGA CD and a third party HDMI expansion adapter could both be plugged in at the same time. It would really be awesome if a HDMI graphics adapter could be added to the side expansion slot without having to internally modify ones existing system.

Edited October 26, 2018 by HDTV1080P

[+-^CrossBow^-]

The side expansion port that was primarily only used for the SegaCD add-on is essentially an extension of the cartridge port and shares many of the data lines from it. There is an external audio line but that is to pull in audio from the sega CD through the Genesis, not the other way around.

[derFunkenstein]

The side expansion port that was primarily only used for the SegaCD add-on is essentially an extension of the cartridge port and shares many of the data lines from it. There is an external audio line but that is to pull in audio from the sega CD through the Genesis, not the other way around.

 

That's definitely true because you can get CD audio out of the Genesis 2 through the RGB plug.

 

I've often wondered why the Sega CD had red and white RCA output jacks on the back. It's got a line in, so I guess you could use a 3.5-mm patch cable to go out from the Genesis and in to the CD, then out from the CD to the TV? That would salvage stereo sound out of the Genesis, but if you were routing the Sega CD audio to the Genesis and then back out (which can be done via the cart port, because I'm pretty sure the 32X does this) then wouldn't the audio be doubled?

 

I guess the RCA jacks don't output the CD audio, just whatever is being piped in?

Edited October 27, 2018 by derFunkenstein

[+-^CrossBow^-]

I've never actually tried it but my understanding is that if you use the RCA jacks off the Sega CD you will get CD audio only from it unless you use the patch/mix cable you are talking about, in which case you get both CD audio and the Genesis audio in one. But it isn't doubled or at least there doesn't appear to be a delay or anything that would cause you to hear the CD audio twice as loud or delay/reverb like that I'm aware of.

 

Then again I don't use the jacks off the Sega CD. I have external RCAs mounted on the rear of my Genesis and all audio including from the 32x passes through those external jacks. Much simple this way wiring wise.

[+chicgamer]

I have a model 1 hooked up to a model 2 Sega CD, and I run a cable from the headphone jack on the Genesis to the Sega CD and then run that audio from the Sega CD to speakers. It works without issue.

Edited October 27, 2018 by chicgamer

[+-^CrossBow^-]

I have a model 1 hooked up to a model 2 Sega CD, and I run a cable from the headphone jack on the Genesis to the Sega CD and then run that audio from the Sega CD to speakers. It works without issue.

 

Yeap and Sega did that so that you could literally use the SegaCD as a CD player. The RCA jacks were put in so you could run the audio out to your receiver system on your home theatre. So again, all audio is processed through the Genesis including the 32x. But if you don't use that mix cable from the model 1, then you only get CD audio as I understand it but I've never used them to test this. I've also heard that the audio between the genesis and CD audio from those RCA jacks isn't quite balance volume wise. Makes sense because on the model 1, using that patch cable would mean that the volume slider effects the volume of the genesis audio but doesn't affect the CD audio on those RCAs. So you have to fiddle with that volume slider to get the right balance. And that likely has to be adjusted from game to game as some games are louder than others.

[+chicgamer]

Right, without the patch cable, you get no Genesis audio from the RCA jacks on the back of the Sega CD. I just keep the volume slider on my Genesis at max. It seems strange to me that Sega never released an official patch cable for this sized to the exact length needed (at least, if they did, I never remember seeing it).

 

Off topic, but a couple of weeks ago, I finally started having issues with my Sega CD. I bought it new in 1995 (I think), so after 23 years, it finally needs some work. I really wish someone would come out with an ODE for the Sega CD.

[+-^CrossBow^-]

Right, without the patch cable, you get no Genesis audio from the RCA jacks on the back of the Sega CD. I just keep the volume slider on my Genesis at max. It seems strange to me that Sega never released an official patch cable for this sized to the exact length needed (at least, if they did, I never remember seeing it).

 

Off topic, but a couple of weeks ago, I finally started having issues with my Sega CD. I bought it new in 1995 (I think), so after 23 years, it finally needs some work. I really wish someone would come out with an ODE for the Sega CD.

Which model segaCD do you have? Most likely the main logic could use a recap. I did mine sometime back. HOWEVER, I also made the mistake of recapping the laser assembly as well since those are included in the kit I got. And... the damn thing would not work anymore after that. Even when I installed the original caps..it refused to move up and down and home in anymore. Had to swap out the laser assembly with another one I has tucked away. So, the only thing I can think of, is that the new caps changed everything electrically so much, that is somehow immediately burned out the laser diode when it was first powered on. No amount of adjustment afterwards would resurrect it.

Edited October 27, 2018 by -^Cro§Bow^-

[derFunkenstein]

Right, without the patch cable, you get no Genesis audio from the RCA jacks on the back of the Sega CD. I just keep the volume slider on my Genesis at max. It seems strange to me that Sega never released an official patch cable for this sized to the exact length needed (at least, if they did, I never remember seeing it).

 

Off topic, but a couple of weeks ago, I finally started having issues with my Sega CD. I bought it new in 1995 (I think), so after 23 years, it finally needs some work. I really wish someone would come out with an ODE for the Sega CD.

 

 

Which model segaCD do you have? Most likely the main logic could use a recap. I did mine sometime back. HOWEVER, I also made the mistake of recapping the laser assembly as well since those are included in the kit I got. And... the damn thing would not work anymore after that. Even when I installed the original caps..it refused to move up and down and home in anymore. Had to swap out the laser assembly with another one I has tucked away. So, the only thing I can think of, is that the new caps changed everything electrically so much, that is somehow immediately burned out the laser diode when it was first powered on. No amount of adjustment afterwards would resurrect it.

 

 

These kinds of stories are why I (as somebody who has no soldering skill) am so excited about 100% (or 99.9999%) accurate clone consoles and will pay the price, but I'll never buy a Sega CD again for fear of this sort of thing.

[+chicgamer]

Which model segaCD do you have? Most likely the main logic could use a recap. I did mine sometime back. HOWEVER, I also made the mistake of recapping the laser assembly as well since those are included in the kit I got. And... the damn thing would not work anymore after that. Even when I installed the original caps..it refused to move up and down and home in anymore. Had to swap out the laser assembly with another one I has tucked away. So, the only thing I can think of, is that the new caps changed everything electrically so much, that is somehow immediately burned out the laser diode when it was first powered on. No amount of adjustment afterwards would resurrect it.

 

I have the model 2. I'll need to look into a recap kit. I hope that's it and it's not the laser (not sure how difficult it is to find a replacement).

 

 

These kinds of stories are why I (as somebody who has no soldering skill) am so excited about 100% (or 99.9999%) accurate clone consoles and will pay the price, but I'll never buy a Sega CD again for fear of this sort of thing.

 

Yeah, I'm really hoping for a Sega CD ODE. I have to think that one will eventually get made, considering all of the consoles that have an ODE now (Turbo CD, FM Towns Marty, Saturn, PS1, Dreamcast, etc).

[derFunkenstein]

 

Yeah, I'm really hoping for a Sega CD ODE. I have to think that one will eventually get made, considering all of the consoles that have an ODE now (Turbo CD, FM Towns Marty, Saturn, PS1, Dreamcast, etc).

 

 

It's the perfect 2020 product for Analogue, assuming the Mega Sg sells well. I'm doing my part on that front.

[Yakumo1975]

Right, without the patch cable, you get no Genesis audio from the RCA jacks on the back of the Sega CD. I just keep the volume slider on my Genesis at max. It seems strange to me that Sega never released an official patch cable for this sized to the exact length needed (at least, if they did, I never remember seeing it).

 

Off topic, but a couple of weeks ago, I finally started having issues with my Sega CD. I bought it new in 1995 (I think), so after 23 years, it finally needs some work. I really wish someone would come out with an ODE for the Sega CD.

In Japan and I'm sure the UK also the Mega CD came with a patch 3.5mm to 3.5mm cable to connect the Mega Drive to the Mega CD.

[Andromeda Stardust]

And just so you are aware, the model 1s tend to exhibit nasty jail bars on the s-video and even RGB signals. Further modification is usually required to try and minimize that as much as possible.

Do not confuse jailbars with composite alpha blending. My Super Retro Trio displayed the jailbar effect when playing the Sonic games over Svideo. I think it's a rather unique effect.

 

If you just want composite, hack a 5-pin DIN Midi cable with some shielded RCAs. The bottom (middle) pin is ground and left / right pins are mono audio and composite video. One of the pins adjacent to ground is +5v. The other is Vsync. Care must be taken when cutting the two unused pins that you don't acidentally short vcc to the ground shielding inside the midi cable.

 

Splicing your own cables will yield a superior signal compared to janky 3rd party cables. I bought an unshielded "Model 1" cable on Amazon that was awful. RF had better picture than composite on that POS. If you have a VA7 Model 1 (I think the most common revision), please mote the mono audio on this specific model has distortion over both the AV Din connector and the rf output. Use the headphone plug with volume set to 5 for a distortion free stereo line out.

 

If you want rgb, you'll need an 8-pin DIN. These are hard to find, and the Genesis has an odd shaped 8-pin DIN connector as the pins form a U shape rather than a 3/4 circle like the Turbografx plugs. The U shaped DIN8 cables are even rarer to find than the circular ones.

 

Analog is doing preorders for a "Mega SG" FPGA clone thst covers all the classic Segas up to and including the Sega CD (Sega CD requires an original drive attachment). If you are holding out for an HDMI mod, you might grab this instead.

[+-^CrossBow^-]

Do not confuse jailbars with composite alpha blending. My Super Retro Trio displayed the jailbar effect when playing the Sonic games over Svideo. I think it's a rather unique effect.

 

I'm really not going to debate this with you. I'm not talking about alpha blending...I'm talking about freaking solid lines of slightly different color against solid sections of color. They are a result of noise coming off the VDP color subcarrier that runs next to the RGB lines. I was able to minimize them to near null by literally cutting and removing that trace as it ran next to the rgb. But of course doing this will cause color errors in the signal with composite and s-video. So...to get around that, I installed a switch to essentially turn that subcarrier on and off. I can also use it to show the jail bars as they appear and disappear on the screen.

 

In fact...the "rainbow banding" that is complained about on the earlier model 1 units, is in fact the jail bars. In composite due to artifacting, they will cause the rainbow like hue of colors. This is easier to see with s-video because while the rainbow color shifting effect isn't there in s-video, the actual jail bars themselves are and are in the exact same place where the rainbow banding effect was seen if you switch over to composite.

 

The va7 model doesn't usually have the jail bar issues at all. However, the sound filtering and amplification is such a mess that I only use the va7 model for spare parts. Yeap...I really dislike the va7 variant.

Edited November 1, 2018 by -^Cro§Bow^-

[HDTV1080P]

The 1982 ColecoVision, 1983 ADAM computer, and 1989 Sega Genesis system all use the exact same Zilog Z80 8 bit microprocessor at 3.58Mhz. However the Sega Genesis only uses the Zilog Z80 3.58Mhz processor as a sound controller for its native stereo sound and to maintain backwards compatibility with the Sega Master system games. Even though the Sega Genesis cartridges are 64 pins the side expansion port uses the exact same 60 pin connector as the ColecoVision and ADAM computer. This means in theory any 60 pin extension cable that works on the ColecoVision/ADAM should also work on the Sega Genesis system. I plugged a 60 pin Coleco style extension cable into the Sega Genesis and it fit, but I do not own any side expansion hardware for the Sega Genesis to see if it works. There might be digital PCM audio coming out of the data lines on the expansion port to offer HDMI digital audio, optical digital audio, or coaxial digital audio that could be sent directly to a A/V receiver and bypass the audio D/A converter for improved sound quality. Some of the Sega games (actually many) are in native stereo sound. It appears that Nintendo and Sega might have gotten some hardware and software ideas from the ColeocVision/ADAM. The ColecoVision/ADAM had several Sega and Nintendo games that played on that classic early 80’s system plus some simlair hardware that was mentioned above.

 

Of course the Sega Genesis System One in 1989 is a much more powerful videogame system when compared to the ColecoVision/ADAM. The Motorola 68000 16 bit CPU that runs at 7.6Mhz on the Genesis is a nice feature that is not offered on Coleco hardware. Plus better graphics on the Sega Genesis System One.

 

I compared the ATARI 2600 Superman to the Sega Genesis Superman and the Superman for the Sega Genesis is outstanding. The ATARI 2600 is a 1977 system and that is understandable why the graphics and sound are not as detailed (I actually owned the Superman Genesis game cartridge from the 90’s that was used on the Pioneer Laseractive system with the Sega Genesis plug in pack). On the ADAM computer some of my favorite games are Buck Rodgers the Supergame, Subroc the Supergame, Donkey Kong the Supergame, and Donkey Kong Junior the Supergame with all 5 screens. Those are all arcade classics that would look and sound better on the Sega Genesis if a programmer were to make those games for the Genesis system.

Edited November 3, 2018 by HDTV1080P

[phoenixdownita]

..... freaking wall of text totally unrelated to the topic .....

You really should stop bringing in anything CV/ADAM into any freaking thread you open .... it's getting old.

 

The CV/ADAM is its own system (or two really), the others are their own systems, stop telling around what a CV/ADAM can and cannot do as it's easy to find out and no-one really cares unless in a CV/ADAM thread (which this one and another dozen you opened are NOT).

 

This one's for you

http://atariage.com/forums/topic/283544-how-good-was-the-coleco-adam-compared-to-other-computers-of-the-time/

go to town, have a party, there you're welcome to put all observations, comparisons and other CV/ADAM related trivia you feel like you want to impose to the unwary reader.

[+Black_Tiger]

What Chicgamer said above...

 

Also a new company I'm quite impressed with also makes good SCART RGB cables for the Genesis systems.

 

https://insurrectionindustries.com/product/

 

They are in the US so quick to ship and slightly cheaper than ordering from overseas.

I was excited to finally have a source for quality cables without having to pay so much for shipping from Europe to Canada.

 

I went through checkout for a single cable and the cheapest shipping to Canada is $32.40 USD. Even more expensive than RGC.

 

The "flat rate" option is $58.35 USD.

 

I'll probably eventually buy their exclusive Gamecube hdmi solution though.

[kool kitty89]

On 10/26/2018 at 9:29 AM, -^CrossBow^- said:

Nothing from it other than being a serial output port for using the Mega Modem at 2400 baud. That is why it was later removed as it was never used here in the states. There ins't any video or audio lines from it by default. However, since it was never used here in the states, you could if you wanted... cut the traces off the board that connect to the pins except the ground as you can leave that in place. And then fashion yourself a cable that has the RCA and s-video jacks etc from it as a break out cable of sorts. In other words you reuse that port to provide additional connections the Genesis model 1 doesn't have on its own currently.

 

And just so you are aware, the model 1s tend to exhibit nasty jail bars on the s-video and even RGB signals. Further modification is usually required to try and minimize that as much as possible.

I don't see pinout diagrams listed online for the EXT port, but I'm almost positive it's a complete Sega Mega Drive controller port, just with the opposite gender. (so a 6-bit parallel port plus serial data signal, I think through the 'select' line normally used to handle the button multiplexing)

 

I don't think much or any homebrew stuff makes use of it either. 

 

http://www.sega-16.com/forum/showthread.php?5129-EXT-port-on-model-1

Quote

TmEE said:08-11-2008 09:59 AM

The EXT port hardware is identical to Controller ports, only difference is the gender of the D9 connector... all ports feature 4800 baud bidirectional serial capabilities (but no handshaking AFAIK) and 6-bit bidirectional parallel, direction of each bit can be configured independently. Its is much feasible to use LPT port rather than COM port, as the voltage levels of PC COM ports are 2x higher than of your MD, and you will kill your MD (at least partially).

 

 

 

On 10/26/2018 at 7:00 PM, -^CrossBow^- said:

The side expansion port that was primarily only used for the SegaCD add-on is essentially an extension of the cartridge port and shares many of the data lines from it. There is an external audio line but that is to pull in audio from the sega CD through the Genesis, not the other way around.

Now that one's pretty easy to find documentation of:

http://www.hardwarebook.info/Mega_Drive_Expansion

 

The expansion connector is much more limited than the cartridge slot, it's only got 17 address lines and lacks address 0, so it's a 16-bit word bus with 256 kB address range.  It's missing a bunch of neat, useful expansion signals the cart slot has and wouldn't be capable of 32x style genlock video overlay because of that, let alone the address space constraints. (the address issue is also why the MD end of things can only see portions of the MCD's memory and hardware in 128kB blocks with bank switching: also making it more difficult to port MD games to the CD)

There'd have been a lot more freedom in interfacing had the normal cart slot been used to interface the Mega CD instead ... though a CD drive module more like the original PC Engine CDROM^2 wouldn't have been limited by that interface and neither would the floppy disk drive add-on Sega had planned to use that port for initially.

 

Sadly, neither the expansion port nor cartridge slot (or expansion port) exposed the 10 data lines needed for the MD VDP's pixel/color expansion bus (which would allow overlaying video in the digital domain and expanding the color palette/CRAM entries) opposed to the more comprehensive expansion port the PC Engine has. (more ironic given NEC opted to circumvent that with the Supergrafx when most/all of those features could've been done efficiently via a modular add-on, including one that simply swapped out the CD drive's base tray; and of course Sega had to jump through more hoops to implement the 32x and couldn't upgrade the native MD graphics output: the Supergrafx didn't upgrade the color depth, but it easily could have)

 

 

 

On 10/26/2018 at 8:04 PM, derFunkenstein said:

 

That's definitely true because you can get CD audio out of the Genesis 2 through the RGB plug.

 

I've often wondered why the Sega CD had red and white RCA output jacks on the back. It's got a line in, so I guess you could use a 3.5-mm patch cable to go out from the Genesis and in to the CD, then out from the CD to the TV? That would salvage stereo sound out of the Genesis, but if you were routing the Sega CD audio to the Genesis and then back out (which can be done via the cart port, because I'm pretty sure the 32X does this) then wouldn't the audio be doubled?

 

I guess the RCA jacks don't output the CD audio, just whatever is being piped in?

The MCD has its internal mixing/output disabled by default (outputs just its internal sound through the RCA jacks and mixes audio through the MD), but when the aux audio input is grounded, it disables the sound going into the MD and mixes the MD audio through its internal mixing circuit, ending up with a cleaner, higher quality output. (moreso when the MD in question has poorer sound amp circuitry)

 

I'm not sure how that works with a MD/Genesis II or if you're stuck with the crappy mixing on the MD side.

 

All MCDs/Sega CDs came with an appropriate mixing cable, too, and all model 2 CD units also came with an extension block for the model 1 MD/Genesis. (also an RF grounding/isolation plate that screws onto the console and locks it into the slots on the CD unit)

 

Early in the MD's life, Sega also offered stereo PC style amplified speakers you could plug into the headphone jack on the model 1 to get stereo sound output.

http://www.sega-16.com/forum/showthread.php?16473-Does-anybody-own-a-set-of-theese

 

 

On 11/1/2018 at 1:07 AM, Kosmic Stardust said:

Do not confuse jailbars with composite alpha blending. My Super Retro Trio displayed the jailbar effect when playing the Sonic games over Svideo. I think it's a rather unique effect.

That's just a type of dithering with the side effect of being easier to compress the graphics and/or end up with more solid looking blending, or sometimes even just looking better without composite video or RF smearing or artifacting. (the waterfalls in Sonic games using that technique tend to look OK through raw RGB or emulators, but plenty of other cases look rather bad)

 Results also vary widely depending on the video encoder used and in NTSC vs PAL. (PAL tends to smear/blend rather than artifact, but NTSC ends up with color errors and 'rainbow banding' in either vertical or diagonal lines across the screen: checkerboard dithering causes diagonal lines, 'strippy' AKA 'column' dithering leaves vertical bands) The effect is limited or absent in the lower res H32 mode (256x224) probably due to a combination of less chroma bandwidth required and the dot clock being a less fractional multiple of the NTSC color clock. (H32 is 5.3693 MHz, 1.5x NTSC 3.5795 MHz, but H40 320 pixel wide mode is at 6.7116 MHz or 1.875x chroma).

 

The Sony CXA1145 encoder commonly used exhibits the rainbow chroma artifacts dramatically in composite video and faintly in S-video. It's also there with the later CXA1645 encoder, but more subtle and almost absent in S-video.

 

The oft-dreaded Samsung KA2195D common to many model 2 Genesis consoles had generally poor and blurry composite output and lacks a luminance signal output (so S-video is impossible to get out of it), but seems immune to the rainbow artifacts and ends up blurring things so badly-but-evenly that dither-bars/strips end up blending very solidly and looking like actual translucency. (I suspect some games were developed with test/dev systems using that encoder, too, with art optimized around what it was outputting) It ends up looking more like really blurry PAL style composite video with horizontal smearing. (but without the vertical color blending/accumulation)

The composite video filter/smear effect that Kega Fusion uses (or used to use) is very similar to what the Samsung chip outputs.

 

I'm pretty sure that only holds true for the higher res H40 mode and H32 has coarse enough pixels to not blend 100%. (though it can be pretty close, and other artifacts aren't as bad, so games like Virtua Racing and some styles of FMV will look better with it)

 

On top of all that there's 2 other things: 1 is analog video noise present in the RGB signal that (depending on the console and the TV, and not limited to the Model 1) has bright/dark vertical line variances on each column of pixels. That could be the jailbars some refer to, but similarly there's also jailbar style dot crawl present in composite video, worse on some TVs than others and generally worst with the Samsung KA2195D video encoder. (this is more often called 'picket fence' artifacts and not jailbars)

I've also seen jailbars show up on some TVs in S-video or through RGB to component video adapters, but some TVs and monitors seem to hide or filter it out better. (CrossBow mentioned it's interference/crosstalk from the NTSC chroma signal, which it could be, but I'm not sure it explains the range of scenarios I've seen it crop up; he also describes it as solid sections of color and not bright/dark shades on the luminance end) 

 

 

On 11/1/2018 at 5:41 AM, -^CrossBow^- said:

 

I'm really not going to debate this with you. I'm not talking about alpha blending...I'm talking about freaking solid lines of slightly different color against solid sections of color. They are a result of noise coming off the VDP color subcarrier that runs next to the RGB lines. I was able to minimize them to near null by literally cutting and removing that trace as it ran next to the rgb. But of course doing this will cause color errors in the signal with composite and s-video. So...to get around that, I installed a switch to essentially turn that subcarrier on and off. I can also use it to show the jail bars as they appear and disappear on the screen.

 

In fact...the "rainbow banding" that is complained about on the earlier model 1 units, is in fact the jail bars. In composite due to artifacting, they will cause the rainbow like hue of colors. This is easier to see with s-video because while the rainbow color shifting effect isn't there in s-video, the actual jail bars themselves are and are in the exact same place where the rainbow banding effect was seen if you switch over to composite.

 

The va7 model doesn't usually have the jail bar issues at all. However, the sound filtering and amplification is such a mess that I only use the va7 model for spare parts. Yeap...I really dislike the va7 variant.

I'm pretty sure the rainbow banding is just NTSC chroma artifacting created by luminance data being mis-interpreted ad chroma the limitations of the video encoders used (typical chroma-luma crosstalk). You have the opposite problem (dot crawl, though on the MD it's typically vertical bars fringing areas of high contrast color, not swarming dots) with chroma corrupting the luma data, but that's only present in composite video and not in S-video. (an artifact created by combining the two signals onto one line rather than inherently created during the RGB to NTSC encoding process)

 

Rainbow banding is almost certainly related to high contrast luminance regions getting mis-interpreted as chroma data in the classic NTSC composite video color phase artifacting sense (the same thing that gives you Apple II, CGA, etc artifact colors) and due to the dot clock being a somewhat ugly multiple of the NTSC chroma clock (15/8) the artifacts aren't solid/consistent at all and oscillate across the screen and fluctuate/flash/shift when scrolling occurs.

The sony video encoders seem to deal with the lower res 3/2x chroma dot clock (mode H32) better and doesn't seem to have that problem, and as I mentioned above, the effect seems totally absent on the otherwise rather awful Samsung unit. (though it has awful picket fence or jailbar style dot crawl artifacts)

 

 

Hmm

http://www.sega-16.com/forum/showthread.php?24968-MD-Genesis-Jailbars-Revisited

 

Skimming that thread, it seems to be an artifact of the RGB encoder itself, but not quite like I thought. It's an issue of the chroma clock (color carrier) signal being used by the encoder at all, and not a matter of interference of signals through traces on the board, but inside the video encoder chip (just disconnecting/lifting the pin on the encoder will basically eliminate the jailbar artifacts but also give you crisp, luma-only black and white composite/s-video ... like on the Amiga 500 TV out ... or if you wire a C64 or Atari 8-bit video cable wrong and put luma on the composite cable ... kind of ironic it was the Amiga and not Atari ST that did that, especially since the ST is way way less NTSC color encoder friendly with that 8/16 MHz dot clock, plus Commodore already had those chroma/luma S-video C64 monitors that'd should've suited the Amiga fine, so it's kind of weird ... granted, also weird Atari put separate Y/C output on their 8-bit computers yet didn't offer a Y/C monitor to exploit that ... or not even crisp/clear grayscale composite video cables using the luma signal alone for nicer/clearer text and sharp grayscale graphics more suited to the 'serious' computer scene ... or just people who wanted less eyestrain)

Err wait, I guess it would be pretty easy to just wire the ST's RGB+synch into a weighted luminance signal via an adapter cable, but I don't think I've seen one of those. (would've been handy for the first-gen 520ST without composite/RF output and on later models if you didn't have an RGB monitor but cared more about picture/text quality than color)

 

Then again, this coming from someone who had a used grayscale VGA monitor on a homebrew multimedia/family PC as a kid in the early 90s. (which worked well enough until we got some games using red/cyan stereo 3D glasses effects ... )