NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/os/mswindo/apps/6158

Text File | 1992-12-16 | 3.0 KB | 65 lines

Newsgroups: comp.os.ms-windows.apps
Path: sparky!uunet!cs.utexas.edu!uwm.edu!linac!att!cbnewse!cbnewsd!att-out!cbnewsh!rkl
From: [e-mail] (kevin.laux)
Subject: Re: Videoblaster only works in Low Resoluti
Organization: AT&T
Date: Wed, 16 Dec 1992 17:08:26 GMT
Message-ID: <[e-mail]>
References: <[e-mail]> <[e-mail]>
Lines: 54

In article <[e-mail]>, [e-mail] (Wolfgang Schwanke) writes:
> [e-mail] (Brad Steele) writes:
>
> >A feature connector allows your graphics card to directly
> >interface another piece of hardware.  It's sort of an expansion for the
> >graphics card.  In the case of the video blaster, that's how the
> >graphics are displayed.  The video information is transferred directly
> >between the "blaster" and your VGA card.
>
> Actually this is not the case. The output of the VGA card is going through the
> normal socket on the rear of your computer back into the videoblaster.
> There the two signals are mixed on *analogue* level in the blaster.
> The VGA monitor has to be connected to the videoblaster instead of the VGA
> card because of this.

    Actually this *is* the case.  There is the normal VGA output through
its 15 pin connector, but this is *not* connected to the VB card.  The VGA
feature connector is used to feed *digital* data to the VB card, which has
duplicated the VGA's 256 DAC registers.  You are correct in that the two
signals are mixed on an analog basis and that the monitor is connected to
the VB card.

> The blaster uses chroma key, all magenta (pink) coloured parts of the VGA
> screen are overwritten with the TV image. The WinVideo prog. just displays
> a magenta window into the VGA, all the mixing is done later.
>
> If for you create a magenta surface (say using Paintbrush) and move it where
> the video window should be, you can see the video "through" the overlaying
> window.

    The VB card does indeed use chroma keying, but magenta is probably
just the default key color, as it can use *any* of 256 keys (and I say 'keys'
because the value is 0 to 255 and is the index into the DAC registers, each
of which can hold one of 2 to the 18th colors (6 bit RGB triplets)).

> The feature connector is merely used for synchronising both cards (I think).

    Not exactly, see above.

> >I find it humorous that they say "not more than 15MB".  Does this mean
> >that it won't run if you have 16MB of ram?  Strange.
>
> All memory above 15 MB will be disabled, but it'll run I guess.

    No, you must either disable memory above 15 MB (with switch or jumper
settings) or physically remove it.  The VB card needs a 1 MB frame buffer that
resides above system memory.  This frame buffer also needs to be mapped into
a memory space less than 16 MB because of the DMA limitation.

--
________________________________________________________________________________
    R. Kevin Laux                Email: [e-mail]
    AT&T Bell Labs                Voice: [phone]
    Holmdel, NJ 07733            Fax:   [phone]