OS4.0 and AGA video mode @31.5 kHz...

[flaviosr]

Hi to all,

I have read in the installation of OS4.0 about the possibility to use the standard video modes of Amiga @ 31.5 kHz without SD!!! True?
I do not have an adapter RGB=>VGA so I ask before buying it...
Is this possible in OS3.9 also?
In this last case... would it be possible to run WHDLoad games without SD?!?!? :-)

[Matt_H]

WHDLoad doesn't work on OS4.

The way screen promotion works is that NTSC screens are changed to DblNTSC screens and PAL screens are changed to DblPAL screens. In OS4 I think the Dbl modes can replace the 15KHz modes, but in 3.9 the double modes are added alongside the 15KHz modes, meaning WHDLoad can still force a 15KHz screen.

There are a very (very) small number of WHDLoad slaves that support setting Dbl screenmodes, however. Probably less than 4.

[flaviosr]

Matt_H wrote:
WHDLoad doesn't work on OS4.

The way screen promotion works is that NTSC screens are changed to DblNTSC screens and PAL screens are changed to DblPAL screens. In OS4 I think the Dbl modes can replace the 15KHz modes, but in 3.9 the double modes are added alongside the 15KHz modes, meaning WHDLoad can still force a 15KHz screen.

There are a very (very) small number of WHDLoad slaves that support setting Dbl screenmodes, however. Probably less than 4.

mmm... a direct question!
Anyway (apart WHDLoad) I could use this "modes" for both OS3.9 and OS4.0... right?
I only need the RGB=>VGA adapter...?

[alexh]

Yes. It will be slow though and as you already know WHDload (or any software which controls screen mode) wont work.

[Boot_WB]

Also, it is worth noting that most LCD monitors won't sync down to 31.5 kHz on low resolutions (eg 640x480).
Although LCD specs state that they will sync down to 31.5kHz, this tends to be only for their native resolutions and some of the more standard PC resolutions (eg 1024x768).

However, most CRT monitors seem to have no trouble displaying low res screens at 31.5kHz.

If you want to use an LCD, you would be best off buying an LCD TV with SCART and using an RGB-SCART cable.

This has all been discussed before, but I think it is worthy of a reminder to prevent any false expectations of using DBLPAL modes on an LCD monitor through an RGB-VGA adapter.

Regards


Rich

[alexh]

I have to disagree. All monitors including LCD's HAVE to support 31KHz for low resolutions to meet the VGA VESA standards. I've never come across one that doesn't.

The vast majority don't do 50Hz vertical sync (DBLPAL), perhaps you are getting confused?

Most LCD monitors cannot do 50Hz but just use DBLNTSC which is 60Hz

[Boot_WB]

@Alex

Hmmm.. interesting. I've never tried using DBLNTSC screenmodes with an LCD, will have to give that a try.
I assume the same would hold true for scandoubler output using NTSC (as opposed to Scandoubled PAL output which also will not generally display)?

Thanks for the info.

[Matt_H]

Most LCD monitors cannot do 50Hz but just use DBLNTSC which is 60Hz

That's a workaround, but since so much old software (particularly games) demands a (Dbl)PAL screen and simply won't work properly with (Dbl)NTSC (apart from just being cut off on the bottom), I'd say it's not a good long-term solution.

[alexh]

Matt, I agree that it's not a good long term solution, but I dont agree with your reasoning.

Almost nothing (except workbench et al) supports ANY DBL mode be it DBLNTSC or DBLPAL. Game compatibility in DBLNTSC over DBLPAL is the least of your worries ;-)

There are perhaps 5-10 games (that I know of) which support mode promotion (i.e. run in a DBL mode) for 99% of games they wont run in anything other than regular PAL/NTSC.

[EDIT]I've just read about a tool called ModePro which could help promote more software to DBL modes that I was aware of.

But you are right, I always encourage people to seek out LCDTV's or buy a scandoubler rather than mess about with DBL screen modes.

[Matt_H]

@ alexh

I was referring to using the 3.9 bootmenu to force a Dbl mode. I assumed it would work the same way as forcing PAL on an NTSC machine, but, granted, I've never tested its functionality.

[alexh]

AFAIK it doesn't but like yourself I am not 100% sure. (Especially having discovered that modepro application)

I've had a scandoubler in one form or another for a long time and it is just ingrained into me from talking to others that it doesn't work.

I would imagine too many games/applications reset the contents of the registers which control those settings.

Otherwise there wouldn't be such demand for scandoublers?