[mythtv-users] RE: [ Matrox G400 ] VGA - SCART cable WAS: Hotwo enable flicker filters

Cory Papenfuss papenfuss at juneau.me.vt.edu
Sun Mar 20 19:46:55 UTC 2005


On Sun, 20 Mar 2005, [ISO-8859-1] Bernd Müller wrote:

> Hello;
>
> I didn't build the cable until yet. But will do next days. Your last posting 
> was
> a little bit scarring me, as you wrote that your informations are "only" 
> hypothetical. Up to this point i've had believed you had build this cable and 
> are using it successfully with the G400. As i've had spent so much  time in 
> the G400 and had also build three different VGA-SCART cables, which all do 
> not worked for me, my motivation was not so high to test an new hypothetical 
> cable. But as Peter wrote he is using this cable, although with a simple CAT5 
> wire, i will now hot my soldering iron.
 	I put the caveat in there because I'm in the US and haven't ever 
personally dealt with PAL or SCART.  As far as I understand it, however, 
SCART basically provides the *opportunity* to drive R/G/B directly, with 
composite sync... so no "conversion" to YPbPr is necessary.  I have built 
my own equivalent circuit for NTSC that encodes to S-vid and had to 
program the modelines accordingly.   Basically, though, all the video is 
the same.  The only potential gotcha is what the trigger voltage on the 
SCART connector is.  If it's TTL like the monitor, you should be set.  I'm 
not completely sure of the spec, but I see a slight bit of weirdness here:
http://www.hut.fi/Misc/Electronics/circuits/vga2tv/circuit.html
http://eab.abime.net/showthread.php?s=&threadid=13037

I'm sure it won't take much to figure out, but there might be an "rbg 
enable" requirement to make it go.  I just assumed that sending RGBS would 
make it go.

> I've to solve an other problem before. I'm not eble to find any valid PAL 
> modeline for X. I tried the following ones
>
> Modeline "768x576" 14.767 768 769 839 945 576 577 581 625 interlace -csync
> Modeline "768x576i" 14.75 768 784 864 944 576 582 588 625 interlace -csync
> Modeline "720x576" 13.875 720 744 808 888 576 582 588 625 interlace -csync
>
> but get
>
> (==) MGA(0): Min pixel clock is 12 MHz
> (==) MGA(0): Max pixel clock is 360 MHz
> (II) MGA(0): PAL TV: Using hsync range of 15.00-80.00 kHz
> (II) MGA(0): PAL TV: Using vrefresh value of 50.00 Hz
> (II) MGA(0): Clock range:  12.00 to 360.00 MHz
> (II) MGA(0): Not using mode "768x576" (bad mode clock/interlace/doublescan)
> (II) MGA(0): Not using mode "768x576i" (bad mode clock/interlace/doublescan)
> (II) MGA(0): Not using mode "720x576" (bad mode clock/interlace/doublescan)
>
> This is a little bit confusing me, because minimal dotclock is 12 MHz. The 
> modes should be all valid. I've i general problems to use any interlaced mode 
> for X. If i try some non-interlaced 720x576 at 50Hz modes with dotclocks around 
> 27 MHz X will accept them. But they are not interlaced. Interpreting the 
> above error message i would say, the G400 is not able to generate PAL 
> dotclocks around 14 MHz. But from web i know the card is capable.
>
 	I've gotten that message before, too, and it pisses me off. 
There's a big different between a mode not working due to dotclock, vs. 
due to interlace.  Since it definately says that it will go down to 12MHz, 
it'd suspect it either can't or won't do interlacing.

> I'm using the latest version 4.1 of the original Matrox driver.
> The importend lines from my XF86Config:
>
> Section "Device"
>  Identifier  "Device[1]"
>  Driver      "mga"
> EndSection
>
> Section "Monitor"
>  Identifier  "PAL TV"
>  HorizSync  30.0-80.0    <-----BAD!  This needs to be set to 15kHz
>  VertRefresh 15.0
>  Modeline "768x576" 14.767 768 769 839 945 576 577 581 625 interlace -csync
>  Modeline "768x576i" 14.75 768 784 864 944 576 582 588 625 interlace -csync
>  Modeline "720x576" 13.875 720 744 808 888 576 582 588 625 interlace -csync
> EndSection
>
 	You need to have HorizSync set to a minimum of 15kHz on whatever 
head you're planning to run the TV on.  Since you've got a dual-headed, 
tvout, beast of a card I'm not familiar with, I suspect there could be 
some other weirdness preventing you from cooking up your wanted modeline. 
It's odd, though, since normally a bad HorizSync line makes modes not work 
due to "horizonal frequency out of range", not "bad mode clock/..."


> The matroxfb support is compiled in the kernel, but X don't use the 
> framebuffer with this configuration. So i assume it dosn't matter.
>
 	*Probably*, but you never know.  I've had weirdness before with X 
and framebuffer arguing.

> At least i would like to use the G400 with this general VGA-SCART cable. The 
> solution with the framebuffer, i'm using it until yet, is frustrating me. 
> First i've spend much time to configure kernel, frambuffermode and X, 
> soldering the special matrox VGA-SCART cable an now i've to notice the whole 
> setup does not work reliable. Changing framebuffermode, setting the registers 
> for contrast, hue ist working in general bu sometimes not. Sometimes i simply 
> get a greyscale or distorted image. Assigning frambuffermode or contrast a 
> seconed time leads to a good image. I don't know if the problem is in 
> hardware or software. But i know a solution using the general VGA-SCART cable 
> has to be more reliable and more flexible 'cause some newer grafic cards, 
> especially the ATI Radeon 7500 and higher, are supposed to be capable to 
> generate valid PAL/NTSC signals
>
 	That's the sort of weirdness I was talking about.

 	I still think that getting it to work out of normal VGA is the 
best option... since like you say it'll work with other things. 
Convincing the matrox card to be normal might be the trouble... :)

-Cory

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
*************************************************************************


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