Connecting Next to Commdore montitor via RGB/VGA

[JamesAndersBanks]

Hello, I realise this could be considered a Commodore question but I think possibly more knowlege is required of the Next hardware output, so I thought I'd try here.

I need to make a cable to connect my Next to a Commodore 1084S monitor. The monitor has two round RGB inputs, one analog and one digital. I'm assuming I need to connect to the digital as the Next surely outputs digital (someone will correct me if I'm wrong).

I know how to make the cable, there's just one pin at the Commodore end that I don't know which to connect to. The pin - and this is for the monitor's DIGITAL input RGB - is labeled INTENSITY on diagrams, but there's nothing labeled RGB on any diagram of the Next VGA output.

Does anyone know if any of the Next pins outputs anything that could be considered "intensity"?

If there isn't one - I see there's lots of ground pins and maybe I just have to use one of those - then I guess this really is a Commodore question!

Thanks!

[Mad Fritz]

AFAIK the digital Input is for the C128 RGB-I signal. The NEXT-VGA output should be analogue.

[JamesAndersBanks]

Thanks for the reply, Mad Fritz. So someone plugging for example a C64 into the monitor would use the analogue input, same we me and the Spectrum Next. The RGB input with the fewer pins.

And the RGB input with the fewer pins doesn't have the intensity pin, so the problem doesn't come up.

That's if I'm interpreting your post correctly.

Thanks!

[Mad Fritz]

Hi there

As later models of the 1084S were not designed for the C64 any more I assume the analogue input is just for the Amiga.
The C64 is normally connected via CINCH, sometimes via an 8-pin-DIN socket. I any case the this signal is also analogue.
The C128 has two video outputs - one exactly like the C64 and one for the 80-column-mode via RGB-TTL ( sometimes called RGB-I or RGB digital). The I stands for the intensity-signal.

In the past VGA was analogue, a special case of RGB-analogue so to speak. Nevertheless Wikipedia says the 1084S can not handle VGA.

There are many different flavors of the 1084S (at least 13!) eg. -P1, -D1, -D2... with slightly different inputs (electrically and/or mechanically).
Could you provide the exact type of your monitor or a picture of the backsides showing the input sockets?
Otherwise I would more or less continue to poke with the finger in the dark

BR / Andy

[Alcoholics Anonymous]

Yes use analog RGB as Mad Fritz points out. The Next generates up to 512 colours using a resistor ladder as you can see from the circuit diagram for CN1 (VGA Video Port):

https://wiki.specnext.dev/Circuit_Diagrams

Make sure you read the few notes below the diagram too.

The Next has to be put into an RGB mode which can be done by holding R during power up. This will get you to the video card test screen so that you can choose between 50Hz or 60Hz refresh rate. 50Hz must be chosen for accurate spectrum video timing as the spectrum is a 50Hz machine.

The Next should be considered a dual 50Hz / 60Hz machine as some Next specific games will prefer to run at 60Hz to get higher frame rates and some ports will prefer 60Hz because the game originates on 60Hz hardware. The switch can be done from software or function key (F3) so you don't have to worry about having to return to the testcard to change that. Examples of the programs that run best at 60Hz include RAMS (which is like MAME but for the Next) and Bubble Bobble which are running the original arcade roms with the original arcade machines being 60Hz. These things do make sure you can run at 50Hz (more slowly) but having a display that is able to swap to 60Hz would be the best outcome. Other fpga cores like Atari VCS, eg, will prefer and may require 60Hz displays.

The difference between RGB and VGA is in the horizontal line frequency (15kHz vs 31kHz "the scan doubler") and in RGB mode the Next puts out a composite sync signal on HSYNC and a steady 3.3V on VSYNC.

[FFoulkes]

In about 1990, I had a 1084S for my Amiga 500. This was the pre-VGA time.
Well, VGA was actually introduced by IBM in 1987, but VGA-PCs didn't become widely popular for home usage until let's say 1992 (Windows 3.1).
So, before that people used Amigas and Atari STs, and for the Amiga I can say, that it couldn't do VGA (although there was an add-on device called "Scandoubler" or "Flickerfixer", which made it possible to connect an Amiga to a VGA monitor).
So, the 1084S wasn't a VGA monitor, it was designed for machines like the Amiga, C128 and C64.
I used it in the early 90s, before I bought my first PC (386 SX-25) and a VGA monitor (in 1994, I think).
So from the 1084S, VGA was a technical progress. As the Spectrum Next has a VGA output, I probably wouldn't bother to connect it to a 1084S (because this could mean trouble), but get myself a VGA monitor and attach it to it.

I think, I'm firing up "FS-UAE" now and start a game of "Hybris", which was my favourite Amiga game I played on the 1084S.

[Alcoholics Anonymous]

So from the 1084S, VGA was a technical progress. As the Spectrum Next has a VGA output, I probably wouldn't bother to connect it to a 1084S (because this could mean trouble), but get myself a VGA monitor and attach it to it.

RGB displays will get you the persistence and blur that some would say the old games were written for. Modern displays are much sharper.

But the other thing is modern panels are no longer analog so even when they support vga, they are sampling the incoming video. If they do it badly (and many do) then this can lead to display artifacts like doubled up vertical columns that have to be mitigated with manual adjustment of pixel clock + phase controls. I have such a panel and although the mitigation is quite successful (I would call the display clean and high quality), if you look carefully you can still find faint artifacts in a few places.

[JamesAndersBanks]

Thank you for the replies, everyone. Here is a photo of the business end!

[JamesAndersBanks]

Again, really appreciate the help.

Personally, I want an old skool experience, I don't need super sharp. Then again, I might as well use the best of the connectors that this monitor does have, which I assume isn't the composite.

I don't have the money or space for a second monitor anyway, so it's this or I don't use the Next! Am concerned though by "this could mean trouble" from @FFoulkes though...? Can I damage the monitor?

Please correct me if I'm wrong on anything of the below.

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

If I'm using the one of the two with the fewer pins, the analog/RGB, I think that doens't have the INTENSITY so my original question is no longer valid.

I'm assuming RGB ie one of the round black inputs, will be better quality than the composite to the left which has red/green/blue combined?

As Mad Fritz says, the monitor can't handle VGA - I need to run the Next in RGB 15Khz mode, in the config.ini I need: scandoubler=0 --is this correct and is there anything else I need to change?

Again in the config, we have 50_60hz=0 --to my knowledge, I leave it at 0 for 50, you'd change to 1 for 60.

[andydansby]

I had always thought if you connected a Sinclair to a Commodore monitor, you’d rip a hole in the Space-Time continuum.

[JamesAndersBanks]

It's worse than typting "google" into the Google search engine. Hence my caution!

[Alcoholics Anonymous]

No, RGB is fine for the Next and I might even use it if I could tolerate a giant crt on my desk The Next is intended for RGB, VGA and HDMI displays. HDMI still has trouble with generating correct spectrum video timing (the display is fine, timed effects like nirvana are not).

The best quality for CRTs is through RGB. Composite and other options have less bandwidth and will show blurring that is a function of the electronics rather than the display itself. Some people have stated they want that too, to go all the way back to the blurry displays and dot crawl of the original machines on their PAL tvs. So there is that

Settings for RGB would be:

scandoubler=0 ;; 15kHz scan lines, otherwise it's 31kHz for vga via scan doubler
50_60hz=0 ;; 50Hz refresh rate necessary for spectrum video timing
timing=0 ;; vga-0 machine speed is not adjusted so will be the same as original spectrum

vga-1 to vga-6 (timing=1 to 6) adjust the machine speed upward in steps so that the refresh rate rises from 50Hz toward 60Hz. This is to accommodate displays that cannot sync to 50Hz refresh rate but vga-0 is the preferred setting.

You can also do these settings by holding "R" on power up to get to the RGB testcard. Then you are choosing between 50 and 60Hz on rgb (vga-0).

For the Next you want the analog / linear RGB interface as the RGB channels are analog. I don't think you can damage any display with the wrong signal; I think you'd just see a garbage display.

I know the 1084 works fine with the Next as others are using it. But there isn't one version of the 1084 -- there are several with different connectors on the back.

[JamesAndersBanks]

Thanks!

Don't quite understand this:

vga-1 to vga-6 (timing=1 to 6) adjust the machine speed upward in steps so that the refresh rate rises from 50Hz toward 60Hz. This is to accommodate displays that cannot sync to 50Hz refresh rate but vga-0 is the preferred setting.


Are you saying that if there are timing problems I can try seven different values for timing?
timing=0
timing=1
timing=2
timing=3
timing=4
timing=5
timing=6
...and use the one that works best?

"but vga-0" -- this is "timing=0" ?



PS I get the point about wanting dot crawl and whatever else, I have a TV that only has RF input, I'm thinking of buying a box that will convert the Next signal (can't recall which output off the top of my head) to RF, I believe it's called an RF modulator box. For coding I'd use the monitor but the RF TV will be fun for playing games.

[Alcoholics Anonymous]

Are you saying that if there are timing problems I can try seven different values for timing?

The spectrum next is still a spectrum underneath and it is a producing a video frame like the original spectrums. That means 50Hz display and a pal like structure to the frame.

Not all displays can sync down to 50Hz, particularly vga displays because vga is only standardized to 58Hz+ refresh rates. Early vga displays sold in Europe could sync to 50Hz because video standards were 50Hz there. Sometimes they were called multisync monitors. vga displays intended for PCs only can only do 58Hz and above. If buying a new vga display you do have to go out of your way to make sure it can sync to 50Hz and this is made harder by the fact many manufacturers don't advertise this and claim their monitors only do 60Hz+ even if they can go to 50Hz. They can't be bothered.

The Next is driven by a master clock that is nominally 28MHz (vga-0). The entire machine runs off this clock -- the cpu clock divided down from 28MHz, the AY clock is divided down from 28MHz, the uart baud rates are divided down from 28MHz, the 50Hz video frame is derived from the 28MHz clock, etc.

If the user doesn't have a vga monitor that can sync to 50Hz, we still want to be able to display something. So the timing settings vga-1 through vga-6 step up the master clock from 28MHz toward 33MHz and since all the internal clocks are derived from this master clock, the machine effectively runs faster. That includes stepping up the video frame from 50Hz refresh towards 60Hz refresh such that these monitors will be able to generate a picture. The spectrum next will still display everything properly and run normally however the machine will be running faster and because of that interfaces with the real world will be faster (sound shifts up in pitch for example). So you want to run at vga-0 which is the normal spectrum speed and you don't want to have to venture too far from vga-0 if possible. The other option is to stay in vga-0 mode and switch to 60Hz refresh rate. In this setting, the spectrum next runs at normal speed but the video frame is changed to a 60Hz one which, among other things, will break timed video effects like nirvana. You could think of this as if it were an ntsc spectrum or a ts2068.

CRTs especially in Europe were designed for 50Hz operation so you should expect vga-0 to work. A possibility is that Pentagon timing may not work on even 50Hz displays as it generates a 48Hz frame (due to a hardware bug in its original design; the spectrum next will construct 48K/128K/Pentagon video frames depending on sw setting for compatibility reasons). If you want Pentagon timing and the display doesn't work on vga-0 you can bump up to vga-1 to speed up the Pentagon such that the refresh rate is ~50Hz. The spectrum next will speed up a little bit but the amount is not perceptible unless you have an original machine next to you to compare since vga-1 is quite close to vga-0.

timing=0 corresponds to vga-0 which is where you want to be and this goes up to timing=6 which corresponds to vga-6 which is a desperate act to get a 50Hz frame on a vga monitor that refuses to sync lower than 60Hz. timing=7 is hdmi.

[JamesAndersBanks]

Thank you for taking the time to explain this in such detail, AA.

The Next is driven by a master clock that is nominally 28MHz (vga-0). The entire machine runs off this clock -- the cpu clock divided down from 28MHz, the AY clock is divided down from 28MHz, the uart baud rates are divided down from 28MHz, the 50Hz video frame is derived from the 28MHz clock, etc.

OK, so because the 50Hz video frame comes from the clock, it's a percentage of it or whatever, increasing the clock also increases the video frame? Since many monitors need 60Hz video frame, you can force the frame rate up to this by increasing the clock. Though you may have to experiment, by the sounds of it.

So you want to run at vga-0 which is the normal spectrum speed and you don't want to have to venture too far from vga-0 if possible.

...because I'm not using a modern monitor that can't sync down to 50. So I don't need/want to increase the speed of the master clock.

vga-6

Is that read as a minus sign, VGA minus six? Or it's just a dash?

[Alcoholics Anonymous]

OK, so because the 50Hz video frame comes from the clock, it's a percentage of it or whatever, increasing the clock also increases the video frame? Since many monitors need 60Hz video frame, you can force the frame rate up to this by increasing the clock. Though you may have to experiment, by the sounds of it.

The video test card is there for experimentation. If you hold "D" down during power up, the machine will test 50Hz hdmi and 60Hz hdmi. If you hold "V" down during power up, the machine will test vga using vga-0 through vga-6 in both 50Hz and 60Hz. If you hold "R" down during power up, the machine will test rgb using vga-0 only at 50Hz and 60Hz (for rgb you would have to manually select vga-1 through vga-6 by editing a file on sd card). While testing, ENTER selects the display mode and N tries the next one. A beep is heard through the audio connector each time a new display is tried.

So you want to run at vga-0 which is the normal spectrum speed and you don't want to have to venture too far from vga-0 if possible.

...because I'm not using a modern monitor that can't sync down to 50. So I don't need/want to increase the speed of the master clock.
Is that read as a minus sign, VGA minus six? Or it's just a dash?

Yes you've got it. Stick with vga-0 or something close and a crt should be fine at vga-0 except maybe the pentagon timing in which case you can bump up to vga-1 if necessary.

vga-6 ("VGA SIX", a dash in there) is just easier to read than vga6 or vga 6. I would call it something else if I could rewind time far enough as its use is not exclusive to vga. It is determining the master clock frequency and the main purpose is to allow incompatible vga displays to be used but it equally can be applied to rgb displays.

[FFoulkes]

The spectrum next is still a spectrum underneath and it is a producing a video frame like the original spectrums. That means 50Hz display and a pal like structure to the frame.

Not all displays can sync down to 50Hz, particularly vga displays because vga is only standardized to 58Hz+ refresh rates. Early vga displays sold in Europe could sync to 50Hz because video standards were 50Hz there. Sometimes they were called multisync monitors. vga displays intended for PCs only can only do 58Hz and above. If buying a new vga display you do have to go out of your way to make sure it can sync to 50Hz

So you mean, the Spectrum Next can't be connected from its VGA-output to any VGA monitor? That would be strange, I think.

The 1084S (at least the version, I've seen back then) can display 50Hz PAL though. I'm in a PAL-country, and a friend of mine used the 1084S as a television, by connecting a VHS video recorder to it (which of course had an (analogue) television tuner built-in).
I remember being disappointed, because I had bought my 1084S as a computer monitor for writing texts for work in a better quality than on a television, and then I found, the 1084S basically just was a television without a tuner. Well, in the end, the 1084S did the job anyway.

My 1084S had a SCART input on its back, to which I connected my Amiga. That's why I can't say anything about RGB.
(By the way: The "Amiga to SCART" cable also worked with ordinary televisions that had a SCART input. It produced a much better image than using the RF-modulator "Amiga 520", which made that device in a way pointless. Unfortunately I only discovered this after having used that RF-modulator for a couple of years. Ouch.)

[Alcoholics Anonymous]

James, this just turned up on discord:

https://www.ebay.co.uk/itm/115014272944

A vga to rgb cable that apparently works for the Next / 1084 combination.

[Alcoholics Anonymous]

So you mean, the Spectrum Next can't be connected from its VGA-output to any VGA monitor? That would be strange, I think.

You can, hence the vga-1 through vga-6 settings to make sure you can.

The problem is the spectrum's video display is no longer compatible with any modern tv standards. So you have to do something about the signal coming out of the spectrum to adapt it to a modern display. Sometimes this is through a frame buffer that resamples the generated image and converts to another video signal. We can't do that in the spectrum next because we don't have a big enough fpga. That means we have to adapt the signal live - as the spectrum generates it, it goes out. No frame delay, no opportunity for arbitrary signal conversion.

rgb and vga are both very forgiving because they are analog standards. You can bend timing considerably and still get a display out. These two display types can accept a spectrum video frame without bastardizing it. There are however further problems with vga in that vga displays are not equal. For one, they may not be able to sync down to 50Hz which is where the spectrum operates. To that we say, ideally you want a vga display that can sync to 50Hz but if you don't have one, we'll still make it work at the cost of speeding up the machine in real time or by accepting a 60Hz frame that has compatibility problems as it breaks the exact relationship in the spectrum between cpu and video frame generation.

hdmi is not compatible at all with the spectrum frame. We have to actually tweak the spectrum video frame to fit hdmi (not the other way around as in rgb/vga). And this has led to the well known issue that although the spectrum next can display on hdmi, games or demos that do timed video effects will not display properly. Fortunately I think we have a solution for this that will be coming in the next several months. The normal solution is to buffer the video signal and resample for hdmi but we can't do that because of the fpga's capacity limitations.

[JamesAndersBanks]

James, this just turned up on discord:
https://www.ebay.co.uk/itm/115014272944
A vga to rgb cable that apparently works for the Next / 1084 combination.

Thanks - sadly, "Doesn't post to Spain" which is where I live. Though, I could look for others on there, or could maybe get a friend to receive it and send it.

However, the monitor arrived and, guess what, it broke, apparently in the mail. I plug it in, the screen remains blank, the power light comes on the fades over several seconds. Why - and can it be fixed? Well, that's a Commodore question, not a Spectrum question so I can't pursue an answer here.

So this post has been a waste of time - except it hasn't because a) I will try to buy another of these monitors next year and b) I'm sure this post will be hugely useful to others, I can't be the only person who ever thought of plugging a Next into a Commodore monitor.

In the meantime, I'm going to try to find out how to connect the Next to this old RF only TV I have. Maybe that's already been discussed on here, I'll take a look.

Again, thank you all for such detailed answers, I'm sure it'll all be useful to many people, and hopefully me in the future.

[JamesAndersBanks]

Just thought I'd mention... The damanged monitor is being returned at no cost to me, so I've just bought another 1084 on eBay, this time without the S so mono, which is fine with me.

So, once again I'm going to be making a cable to connect it to my Next, so the above will all be immensley useful once again, unless this one gets damaged too!