IC - VGA to PAL

[Jasen Betts]

On 2010-02-17, Sylvia Else <sylvia@not.at.this.address> wrote:

On 17/02/2010 10:34 PM, fuzzymonkey wrote:
From the datasheet:
"The AD725 can be used to convert the analog RGB output from a
personal computer's VGA card to the NTSC or PAL television
standards. To accomplish this it is important to understand that
the AD725 requires interlaced RGB video and clock rates that
are consistent with those required by the television standards.
In most computers the default output is a noninterlaced RGB
signal at a frame rate higher than used by either NTSC or PAL."

They sort of imply that at least some VGA cards can be configured to
produce interlaced output with NTSC or PAL compatible timing, but I've
never come across any information about so configuring them.

the following are for Xwindows but alternatives exist for most other
platforms.

After ModeLine and "the label" the fields are pixel clock (in MHz), displayed
pixels, hsync start, hsync end, total pixel cout for row, displayed rows,
vsync start, vsync end, vertical total, then option flags

(begin modelines stolen from the mythtv website.)
===============

#702x576 @ 25Hz, 15.6kHz, itu-r bt.470 PAL, analog broadcast
ModeLine "702x576@25i" 13.5 702 722 785 864 576 581 586 625 interlace -hsync -vsync

# 704x576 @ 25Hz, 15.6kHz, itu-r bt.470 PAL, mpeg, 702 dots displayed
ModeLine "704x576@25i" 13.5 704 723 786 864 576 581 586 625 interlace -hsync -vsync

# 720x576 @ 25Hz, 15.6kHz, itu-r bt.601 PAL, mpeg
ModeLine "720x576@25i" 13.5 720 732 795 864 576 581 586 625 interlace -hsync -vsync

# 768x576 @ 25Hz, 15.6kHz, square dot itu-r bt.470 PAL, TV-monitor,
767 dots displayed
ModeLine "768x576@25i" 14.75 768 789 858 944 576 581 586 625 interlace -hsync -vsync

# 720x576 @ 50Hz, 31.25kHz, itu-r bt.1358 625/50/p/1:1, RGB, YPbPr, HDMI
ModeLine "720x576@50" 27 720 732 795 864 576 581 586 625 -hsync -vsync

=============
(modelines stolen from the mythtv website end.)

It makes one think that IBM designed the Video Graphics Array to
be capable of producing a video raster.

bye.

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[fritz]

"Sylvia Else" <sylvia@not.at.this.address> wrote in message
news:4b7c7f79$0$1511$c3e8da3@news.astraweb.com...

On 18/02/2010 7:55 AM, fritz wrote:

"Sylvia Else"<sylvia@not.at.this.address> wrote in message
news:4b7bdb98$0$10533$c3e8da3@news.astraweb.com...
On 17/02/2010 10:34 PM, fuzzymonkey wrote:
From the datasheet:
"The AD725 can be used to convert the analog RGB output from a
personal computer's VGA card to the NTSC or PAL television
standards. To accomplish this it is important to understand that
the AD725 requires interlaced RGB video and clock rates that
are consistent with those required by the television standards.
In most computers the default output is a noninterlaced RGB
signal at a frame rate higher than used by either NTSC or PAL."

They sort of imply that at least some VGA cards can be configured to
produce interlaced output with NTSC or PAL compatible timing, but I've
never come across any information about so configuring them.

It's called TV OUT or something similar. Pretty straightforward, really.
Either your video card has it or it doesn't, simple.

A TV out socket will produce a composite video signal. A VGA output with
TV compatible timing would still produce an RGB output with separate
horizontal and vertical sync signals, but the timing would be such that it
could be converted by a circuit such as AD725 into a composite video
signal.

So they're different, and the "either has it or it doesn't" position
doesn't stand up.

Just buy the right video card and stop trying to convert the wrong one.

Simple - either it has it or it doesn't.

 

[fuzzymonkey]

It's a laptop so can't install a new graphics card.
Money is limited so i can't buy a new laptop with TV out.
Space is limited so i can't assemble a PC with a card that has TV out
because it won't fit.

I see your point about wasted effort... but this stuff interests me and i
want to learn as much as i can about it

Just buy the right video card and stop trying to convert the wrong one.

Simple - either it has it or it doesn't.

 

[fuzzymonkey]

--------------------------------------------------
From: "Jasen Betts" <jasen@xnet.co.nz>
Sent: Thursday, February 18, 2010 6:55 PM
Newsgroups: aus.electronics
Subject: Re: IC - VGA to PAL

but seriously with a VGA card, it's just a matter of setting the right
parameters. how are you setting the current video mode?
(mswin? X? libvga? stm?)

I don't know what stm is, but i'm actually running in DOS (I just need a
non-multitasking OS because timing is super critical)

On this page http://www.epanorama.net/circuits/vga2tv/psergio_circuit.html
(it's ancient)
I used this program: http://www.epanorama.net/circuits/vga2tv/vgatv2a2.zip
to convert the video output to an interlaced signal. IT WORKS! but the hsync
signal is inverted!! My old CRT can display the picture, but nothing on the
little Psone LCD. I don't think it can make sense of it.

Can't believe i don't have anything here that can invert the hsync signal!

 

[Jasen Betts]

On 2010-02-26, fuzzymonkey <fuzzymonkey87@hotmail.com> wrote:

--------------------------------------------------
From: "Jasen Betts" <jasen@xnet.co.nz
Sent: Thursday, February 18, 2010 6:55 PM
Newsgroups: aus.electronics
Subject: Re: IC - VGA to PAL

but seriously with a VGA card, it's just a matter of setting the right
parameters. how are you setting the current video mode?
(mswin? X? libvga? stm?)

I don't know what stm is, but i'm actually running in DOS (I just need a
non-multitasking OS because timing is super critical)

"SVGA Text Mode" with a couple of hours work the linux source can be
compiled with the free version of turbo-c for dos. like the label says,
text mode. DOS on a TV

On this page http://www.epanorama.net/circuits/vga2tv/psergio_circuit.html
(it's ancient)
I used this program: http://www.epanorama.net/circuits/vga2tv/vgatv2a2.zip
to convert the video output to an interlaced signal. IT WORKS! but the hsync
signal is inverted!! My old CRT can display the picture, but nothing on the
little Psone LCD. I don't think it can make sense of it.

Can't believe i don't have anything here that can invert the hsync signal!

hsync inversion can be done with software... or a transistor.

bye.

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