I'm pretty sure there won't be any software way to achieve this, there isn't a blank out every other line feature in VGA doublescan mode and there isn't a line interrupt either that could be used by a TSR to blank stuff out every other line.

Tiido wrote on 2022-11-26, 04:09:

I'm pretty sure there won't be any software way to achieve this, there isn't a blank out every other line feature in VGA doublescan mode and there isn't a line interrupt either that could be used by a TSR to blank stuff out every other line.

Thanks a lot for your reply. I was reading EGA programming details but your reply confirm that must be any software

For now i attached a TV, a vga>rgb scart and enjoy real 15khz ega and cga, but still miss have all in same.monitor

I will try to find a 15-31khz screen

Thank you very much! ^^ I've never heard of this utility before.

Just found out its name means "green" in English, also. Cool. 😎

It's really useful, I think - back in the day, a lot of people had monochrome CGA, actually.

Some reasons why:
a) CGA's colour palette was eye straining 😉
b) because monochrome video monitors were affordable and provided good video quality
c) because foreign monitors didn't decode CGA's NTSC signal.
d) because most PC clones had a monochrome video output on their RCA/Cinch connector (no colour burst circuitry)

Ok, technically, PAL<->NTSC transcoder chips existed in the 1980s.
But they were rather rare and didn't convert the sync rates 50 Hz / 60 Hz, just the colour encoding.

PAL/SECAM video monitors, on the other hand, could display 60 Hz video directly in monochrome, if adjusted (V-Hold or H-Hold knobs).

Some games even used the brightness levels of the four CGA colours as matching shades of gray.

@Tiido Thanks for the explanation, too.

There's an alternative to a 15-31 KHz monitor, too.
Converters exist which convert an 15KHz CGA/EGA signal to 31,5KHz VGA (CGA2VGA ?).
At least timing-wise, they're compatible with real CGA/EGA.

They may not accept TTL signals, since they were made for analog RGB (like Commodore 128), rather than digital RGBI.

However, it may still indirectly work, partly, if the TTL signals overdrive the inputs (full on instead of various intensity levels) - at cost of of a few colours.
So ideally, another adapter/converter might be needed here.

To get scan lines, another device is sadly needed, though. Say, SLG3000. 🙁
And maybe a sync stripper is needed, too. 🙁

..
Then, there's a passive VGA adapter which converts colour VGA to monochrome.
It's sending a monochrome picture to one of the individual R/G/B lines.

https://blog.tindie.com/2022/05/monochrome-vg … -color-schemes/

VGA can do create a monochrome conversion of colour on its own.
Not sure if the adapter is using a VGA cards's pin12 for that purpose (pin12= the monochrome monitor detection). 🤷‍♂️

Same could be done with a VGA to SCART cable, I guess.
VGA's CRTC can be configured for 15 KHz video.

https://www.geocities.ws/podernixie/htpc/cables-en.html

Edit: Text removed. I was a bit confused.
"Sync on Green" maybe is an issue if we want to use CVBS/Composite signals for an all green image.
A VGA DIY cable can provide a pure monochrome signal, however, by contrast.

..
Also, there are VGA cards which have a 9pin TTL port next to 15pin VGA.
They can be used as a substitute to a real CGA or EGA card, if really needed. (Except Composite CGA)

Since most early VGA cards (Trident 8900, Paradise, OAK etc) have software-controlled emulation modes for CGA, EGA or Hercules built-in, this should work.

The DIP switch used to select the monitor type should activate the corresponding emulation mode - if no VGA or Multisync monitor is selected.

..
The nice thing about EGA is its close relationship to VGA, I think. Or vice versa.

In mode 12h (640x480 Standard VGA), VGA uses the same 16 colours as EGA by default, for example.

Both EGA and VGA have their own video BIOS, too.
Their control ports are similar, AFAIK.
- That's one big difference to CGA also, I suppose. It has different ones.

Maybe that's another reason why VERDE can instruct the VGA card to alter the CGA image.

(AFAIK, EGA/VGA can also listen to CGA ports for compatibility reasons, though some commands are ignored. Also due the lack of a real Motorola CRTC. Edit: Emulation mode excepted, it can simulate the Motorola CRTC partially)

Tiido wrote on 2022-11-26, 04:09:

I'm pretty sure there won't be any software way to achieve this, there isn't a blank out every other line feature in VGA doublescan mode and there isn't a line interrupt either that could be used by a TSR to blank stuff out every other line.

You can disable the double-scanning bit even in modes that enable it by default. That seems to be just what that 'VERDE' program does if you enable the scanlines option.

The vertical CRTC parameters have to be set accordingly, and for a full-screen picture you'll end up with a doubled (or nearly so) vertical refresh rate. Very far from standard VGA, but that program seems to be targeted at latter-era CRTs, and they can mostly deal with 120Hz+.

That assumes you have a 15kHz capable monitor, which majority of monitors are not, and doing frame doubling to get back to 31KHz is a double edged sword. The artifacts from it make any scrolling game more or less unplayable, as soon as there's motion you get a blurry mess (I even did a black frame insertion mod to counter it on a 100/120Hz frame doubling TV, witch great success 🤣).

A lot of early VGA monitors sync at 31.5kHz, even if the sync signal is just 15.75kHz. So if you can double the horizontal total register (without overflowing it) and make sure the overscan color is black, you can just append a black line after every image line. The sync pulse after the black line is missing, but if the monitor syncs at twice hsync, you will get the scanline effect working on many standard VGA fixed-frequency monitors. I don't accept any blame for blown monitors, though, although I never heard of a VGA monitor that doesn't use a PLL with limited capture range.

theelf wrote on 2022-11-24, 17:45:

Greetings, someone knows exist some software that make scanlines to EGA modes? similar to verde for CGA […]
Show full quote

Greetings, someone knows exist some software that make scanlines to EGA modes? similar to verde for CGA

http://www.abadiadelcrimen.com/verde.html

and 3.0 with ambar, white, blue..

http://www.360k.es/?p=58

I know i can use a scanline generator, or connect a 15khz screen, but i was thinking in a software solution

thanks

There are definitely ways to do it with emulation. The easiest way would be a scanline filter, but you can also emulate the display timings and output to a CRT monitor (well double the framerate but still good ol' fat scanlines).

mothergoose729 wrote on 2022-11-28, 18:17:

theelf wrote on 2022-11-24, 17:45:

Greetings, someone knows exist some software that make scanlines to EGA modes? similar to verde for CGA […]
Show full quote

Greetings, someone knows exist some software that make scanlines to EGA modes? similar to verde for CGA

http://www.abadiadelcrimen.com/verde.html

and 3.0 with ambar, white, blue..

http://www.360k.es/?p=58

I know i can use a scanline generator, or connect a 15khz screen, but i was thinking in a software solution

thanks

There are definitely ways to do it with emulation. The easiest way would be a scanline filter, but you can also emulate the display timings and output to a CRT monitor (well double the framerate but still good ol' fat scanlines).

Since you guys mention both EGA and emulation here.. A few days ago I stumbled over the site of a Japanese emulator writer, Mr. H.Kanemoto.

He too has fond memories of EGA. EGA was the reasons he began writing emulators.

Here's the automatic translation:

"EGA
It was thanks to the graphics device EGA used in PC/AT compatible machines that I first became convinced that an emulator could be created.
CGA/EGA/VGA/SVGA and subsequent compatible graphics devices were compatible at the BIOS level and could be used on any machine.
The EGA's text mode had a function similar to the text attribute function of the PC-8001, 8801, and 9801, and it was possible to change the displayed font externally.
With this, the PC-8001 and PCG fonts can be dynamically changed by the program, and the display can be performed at high speed because it does not use graphics.
So I started developing the N80 for DOS."

Source: http://home1.catvmics.ne.jp/~kanemoto/n80/index.html

VileR wrote on 2022-11-27, 22:23:

You can disable the double-scanning bit even in modes that enable it by default. That seems to be just what that 'VERDE' program does if you enable the scanlines option.

The vertical CRTC parameters have to be set accordingly, and for a full-screen picture you'll end up with a doubled (or nearly so) vertical refresh rate. Very far from standard VGA, but that program seems to be targeted at latter-era CRTs, and they can mostly deal with 120Hz+.

Yep most of the digitally-controlled multisync CRTs will happily display a 31.5khz / 120hz video signal. Sadly it's not very authentic because the scanlines end up very very thin, as these CRTs were designed for high resolution modes and have a correspondingly fine dot pitch.

Also, it's just on the edge of possible to coax a standard VGA into producing a 640x600 mode (37.5khz horizontal and 60hz vertical) using the 28mhz dot clock. The horizontal timings are tight but a good CRT can handle it. If you can then output a frame where each of the 200 EGA lines is doublescanned and then followed by a completely blank line the result is pretty darned close to a real 15.7khz monitor.

Starting from a 640x200 graphics mode and tightening up the horizontal timings, then programming CR09 for a 3-scanline high row and also setting CR17 bit 1 (the "Hercules emulation" mode that sets MA[14] from RA[1]) is so tantalizingly close: the VGA will scan each line three times (due to CR09), the first two times will scan out the video memory address where MA[14]=0 and the third time will scan out the video memory address where MA[14]=1. If you could somehow ensure that the lines where MA[14]=1 were always zero........

(but you can't, at least not by sticking to standard VGA registers, although you'd think maybe fiddling with the odd/even and chaining modes and setting the CRTC to word or doubleword sized addresses might do the trick, it doesn't actually get you where you need to be)