riscy
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Re: Radical video idea

To: riscy@pyramid.com
Subject: Re: Radical video idea
From: Steven.D.Ligett@Dartmouth.EDU (Steven D. Ligett)
Date: 29 Jun 93 14:16:03 EDT
First -- there are too many ideas zooming by for me to sort through them all. 
For now, I'll concentrate on video.  Other facets later.

I think that the idea of having a 3041 generate the video syncs IS too
radical, but is the kind of thinking needed to come up with clever designs. 
Let me expand a little on the video system I was thinking about.  Here is the
list of parts needed for the video system:

2 Mac-compatible 512K VRAM SIMMS  $30/ea
1 TI tlc34076 RAMDAC              $32/ea
1 NSC LM1882 Video sync generator  $8/ea
                                 ----
total                            $100

VRAM appears to the processor as DRAM.  No differences, really.  However, you
can't easily find 60 ns VRAM, and I can get 8MB 60 ns DRAM SIMMs for <$300
any day of the week.  Which is a long way of saying that the VRAM bank(s)
will have different timing from the DRAM bank(s).

The 34076 handles 1, 2, 4, 8, 16, and 24 bits per pixel.  1, 2, 4, and 8 are
translated by a table into 24-bit pixels.  The 34076 completely handles the
serial (video) side of the VRAMs, having only to be set up once to tell it
exactly what to do.  The 34076 does not generate hsync, vsync, blank.

The 1882 generates hsync, vsync, and blank.  Just tell it once what the
timing is to be.

Once the registers in the 34076 and 1882 are set up, the processor(s) just
read and write the VRAM.

For rock-steady video, drive it from a crystal oscillator.  I expect that
there will be a 80 mhz oscillator on the board, so use that.  Giving 1024 x
768 pixels at 72 fps.  Leave space at the 34076 for other oscillators so
folks can use other resolutions - the 34076 can handle 5.

 

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