Do old 15Khz Arcade CRT monitors have only 240 vertical line

[nes.og]

I noticed that the specs for old CRT arcade monitors note they have 240 vertical lines. Did the CRTs do 240P with just 240 progressive vertical lines or were they like consumer CRT TVs with 525 vertical interlaced lines? In this case I know that special timing signals would be used as to not alternate between even and odd lines to display 240P (what Nintendo referred to as “Double Strike”)

Any info is appreciated!

Edit: I should have said “vertical resolution” with only 240 lines total opposed to “vertical lines”. I was referring to the number of horizontal lines counted top to bottom.

[LukeEvansSimon]

You meant to say “horizontal” instead of “vertical”. I bet the specs were just referring to 240p and there is nothing special the arcade CRT is doing that makes it different from 15khz CRT TVs.

[nes.og]

240P refers to 240 vertical progressive lines. 15Khz refers to the horizontal scan rate. TVs were made to NTSC spec (15Khz 480i) so used special signaling for 240P that repeatedly used the same field to display video while not displaying anything on the other field (aka “Double Strike”)

Speaking with others I believe that the old arcade CRTs were able to display just 240 progressive lines because they had different circuitry to output different signaling since didn’t need to support interlaced NTSC.

Edit: I should have said vertical resolution

[headlesshobbs]

I wouldn't be surprised if some were incapable of doing full on interlaced because of the way they were designed to work. Something about this makes me think that 240p at the hardware level with this limitation in mind means double strike is not only undoable, but these displays would be stuck at 30fps standard.

I would be curious if pushing beyond these limits would cause any major damage as a result?

[Sumez]

I definitely had an arcade cabinet at one point that was incapable of 480i, I'm thinking that was pretty common on 80s cabs.

[nes.og]

Thanks for your responses. So it seems they were true 240P with just 240 lines? This is why scan lines don’t seem to be as pronounced as consumer 15Khz interlaced CRT TVs with Double Strike? Does this just come down to signaling since CRTs don’t have fixed line count like LCDs? Where the CRTs themselves also different on a hardware level? If no it would seem possible to interface a 15Khz consumer TV to display the same? Of course you would also need to RGB mod.

[Sumez]

15khz consumer TVs usually don't have any problems displaying 240p signals.

[nes.og]

(Double post: mods can delete)

[nes.og]

15khz consumer TVs usually don't have any problems displaying 240p signals.

Just 240 progressive lines opposed to 480 interlaced Double Strike? This is accomplished with a Super Gun? Also possible with Jungle RGB mod?

[headlesshobbs]

15khz consumer TVs usually don't have any problems displaying 240p signals.

So what happens if we try double strike on these arcade monitors...?

[nes.og]

I would think it would be possible if there is a method to interface to send the same NTSC 480i signals to the Arcade monitor.

[Fudoh]

Just 240 progressive lines opposed to 480 interlaced Double Strike?

that's the same thing - just different names for it. And in regards to 240p vs. 480i: both signals have 60 fields/frames consisting of 240 lines each. A simple half-line offset on the first line makes the display show one with alternating field offsets (interlaced) and the other without an offset between the fields (progressive). Both signals show 60 motion phases per second.

It's certainly possible that some monitors were not able to handle 480i due to those subtle differences, but the majority of monitors was/is ok with both. Enough classic arcade boards from the 80s were running in 15khz interlaced mode instead of 240p.

[nes.og]

You are explaining to what I believe I already have in my previous posts which I refer to as “Double Strike” for simplification like Nintendo did. There would be a difference between the two CRTS because one of them would be 240P with only 240 lines total so it would not have the thicker black scanlines on every other line which is necessary to display 240P on a 480 interlaced CRT.

[Sumez]

I think you're thinking of it in the same sense as modern LCDs where there are scanlines that get either filled out or not, but that's not how it works.

There isn't a scanline on a CRT that's fixed to a specific position, and the alignment of them can often be changed by operator settings or adjustable pots. If you know what you're doing you can potentially take the tube of a raster CRT and convert it into a vector monitor, so the lines aren't even horizontal anymore.

[nes.og]

I mentioned earlier that CRT’s don’t have fixed lines like LCDs and I believed that different signals to the CRT can change the vertical line count which is how they achieved just 240 progressive lines so no Double Strike required to display 240P because not 480i which was required bu consumer TVs for NTSC. Now the question is how to display the same way on a consumer CRT. Super Gun? 240P signal direct to RGB Jungle Chip inputs?

[maxtherabbit]

240p is 240p, there is no such thing as "240p without double strike" that's just nonsense

[nes.og]

240p is 240p, there is no such thing as "240p without double strike" that's just nonsense

Jeez, you don’t have to mean about it lol.

So you are saying the arcade CRTs were also interlaced with the same amount of lines and displayed 240P using the same technique (Repeatedly just displaying one interlaced fields and skipping the other)

Then Arcade monitor spec sheets and resources such as the below must note 240 lines when really 2x more since just 240 lines are used (one of the two interlaced fields)

https://www.arcade-museum.com/monitor.html

[Fudoh]

Repeatedly just displaying one interlaced fields and skipping the other

this never happens. As said above: both 240p and 480i have the same number of fields/frames. And each one is displayed exactly once. The only difference is the vertical offset between the odd and even fields, which doesn't exist on a 240p signal.

[nes.og]

Repeatedly just displaying one interlaced fields and skipping the other

this never happens. As said above: both 240p and 480i have the same number of fields/frames. And each one is displaed exactly once. The only difference is the vertical offset between the odd and even fields, which doesn't exist on a 240p signal.

I’m ultimately just saying one interlaced frame has video and the other frame always black scanlines but from HD Retrovision:

“Older game consoles didn't have the technical capabilities of generating a full 480 line picture. The solution is to assume that a standard interlaced half picture (480 divided by 2 = 240) is a full picture, and simply display this picture at a normal field-rate of 60 times per second. This means that the other field and its entire set of lines are completely ignored. To accomplish this, the "special timing signal" mentioned above is slightly changed to tell the CRT to not alternate between its odd and even lines. Nintendo's name for this type of scanning is "double-strike", because the same set of lines are drawn twice within one scanning cycle while the lines that would normally be drawn in-between them are absent (or not "struck" at all). The more common term used for this type of signaling is "240p" (p = progressive). Another name for progressive is "non-interlaced".

https://www.hdretrovision.com/240p

[Fudoh]

I’m ultimately just saying one interlaced frame has video and the other frame always black scanlines

I understand what you're saying, I just don't know where you're getting this from, since - to quote the old hare up there - that's nonsense.

The Retrovision FAQ excerpt starts out right and ends right as well, but that middle part is wrong, or at least worded in a very misleading way. Ste was probably plain out drunk when writing this.

[Unseen]

I’m ultimately just saying one interlaced frame has video and the other frame always black scanlines but from HD Retrovision:

No, you misinterpreted that quote, but it is not a good one anyway. In both 240p and 480i, every frame contains video.

Both 240p and 480i send 240 active lines of video to the display during a time interval that lasts 16.7ms (~1/60 of a second), so the image on the screen gets redrawn 60 times per second. In fact, if you just capture the signal for exactly one such redraw interval, you would not be able to tell if it is a 240p or 480i signal.

The difference between the two is only visible if you look at two consecutive redraw intervals: For a 240p signal, they both have the same structure, but obviously could show different content, i.e. a moving object. For a 480i signal, there is a small structural difference in the signal that tells the monitor "start displaying this refresh interval at the top position" or "start showing this refresh interval a bit lower than the top position". By convention, the monitor is constructed/adjusted so that when it switches from drawing one line to the next, it leaves a bit of space between the two. Since 240p uses the same "start drawing from there" instruction in every redraw interval, this space stays empty all the time and tends to look dark or black - the well-known "scanline effect". With a 480i signal, the toggling of the "start drawing from here" instruction makes the monitor draw every redraw interval in the space that it left free in the previous one. This is the reason why the technique is called "interlace": Lines from different refresh intervals are interlaced/interwoven to build a full picture, using the persistence of a CRT and the "slowness" of the human eye to build a complete picture.

This method was invented because it improves the apparent resolution in static parts of the image without needing more bandwidth to actually transmit the full resolution in every single redraw interval. There were in fact some early analog HDTV transmission standards that used even more complex interlacing schemes to combine more than two refresh intervals to increase the resolution of static parts of the image even further. Many old game consoles did not use interlacing since the vertical resolution of a single refresh interval was considered sufficient and there can be a noticeable flicker if such a low-resolution image is shown using interlaced lines without any additional processing.

You may have noticed that I tried to avoid the term "frame" in this description: This is because the broadcast industry has decided many decades ago that "frame" should refer to the full-resolution image and "field" should refer to a single refresh interval when interlacing is used. Thus, a 240p signal contains 60 frames per second (and technically no fields at all because it is not interlaced) while a 480i image contains 60 fields per second, two of which are needed to construct a complete frame - it is a matter of interpretation and content if that should mean that a 480i signal has 30 or 60 frames per second.

(Disclaimer: May contain half-truths for simplification purposes)

[nes.og]

I think it nonsense that you’re calling in nonsense lol.

One field is displayed repeatedly while the other is not by using non standard signaling . I’ve seen this documented in numerous places online.

What do you mean by “The only difference is the vertical offset between the odd and even fields, which doesn't exist on a 240p signal”

[Fudoh]

One field is displayed repeatedly while the other is not by using non standard signaling . I’ve seen this documented in numerous places online.

and you think reading false information over and over makes it better or even right?

What do you mean by “The only difference is the vertical offset between the odd and even fields, which doesn't exist on a 240p signal”

unseen describes it quite nicely above. While on a 240p signal line 1 of each frame is always drawn on the same vertical position, lines 1 of two adjacent fields of a 480i signal are drawn with a vertical offset betweem them.

[nes.og]

Seems like we are explaining the same thing. Semantics aside my biggest question was if 15K Aracde CRTs display 240P in the same way 15Khz TV do.

Let’s all be friends

[Fudoh]

yes, they do

[nes.og]

yes, they do

Thanks homie

[NoAffinity]

Arcade monitors can do 480i. Plenty of folks using ulitmarc products to run og xbox and ps2 in their arcade cabs, myself included....or at least did in years past before more current solutions like groovymame/arcade osd, etc.

Before I knew anything about anything, I always wondered why the image seemed softer or fuzzier when running my xbox on k7000 25", didnt realize it was interlaced vs what I was used to seeing when running arcade boards (progressive). I currently run a mame pc in a different arcade cab but also a k7000 25". Windows outside of the front end displays 480i. It is very shimmery and obviously interlacing.

Sent from my SM-G955U using Tapatalk

[nes.og]

According to the others it seem all 15Khz arcade CRTs are 480i just like consumer CRT TVs so can do 240P with the method discussed or 480i just like the TVs

[Josh128]

Currently running an Ultimarc MAME system on my Mace cab using a k7000 monitor (probably the most ubiquitous 25" arcade monitor of all time) and it displays fine 480i in Windows desktop or any MAME games that run higher than 15KHz resolutions.

Also, my 27" Wei-ya Tri-sync can run 480i-- and if you adjust the geometry correctly, its one of the finest native 480i signals Ive ever seen, almost looks progressive.

[nes.og]

Currently running an Ultimarc MAME system on my Mace cab using a k7000 monitor (probably the most ubiquitous 25" arcade monitor of all time) and it displays fine 480i in Windows desktop or any MAME games that run higher than 15KHz resolutions.

Also, my 27" Wei-ya Tri-sync can run 480i-- and if you adjust the geometry correctly, its one of the finest native 480i signals Ive ever seen, almost looks progressive.

Thanks for sharing, that’s awesome that you own a K7000. It is one of the monitors that made me think that some may just have 240 lines total because that is what the specs note in the user manual. I now know that they were just referring to progressive scan opposed to interlaced. Upon doing further research I believe that the K7000 was used at 480i for Nintendo’s Popeye.

So are you saying you can run 480P 31KHz games at 480i and they still look fine without flicker?