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Re: Video on the motherboard

To: riscy@pyramid.com
Subject: Re: Video on the motherboard
From: tim@ubitrex.mb.ca (Tim Braun)
Date: Tue, 6 Jul 93 12:08:54 CDT
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
> The question is whether to put the video on the motherboard or not.

> First, video on the board:

I'd like video on the board.  With the following options:
  1.  640x480 monochrome (VGA compatible) o/p.  Simplest
      anything-should-sync output.
  2.  1024x768 mono SVGA o/p.  Most SVGA monitors should
  3.  1152x900 mono.  The mega-pixel display.  Efficient
      use of memory.
  4.  colour - well, I guess someone's going to want this. 
      8-bit colour versions of the above modes.  This requires
      more memory bandwidth (likely VRAM and interface) and
      and a RAMDAC.  Personally, I don't want to spend money
      on these, but I can see the advantages of colour, and
      appreciate that this is desirable.

The nice thing about mono is we can do the support with
the 3730 alone, and the bandwidth requirements are low
enough to do it in main memory, no VRAM required.  You can
still connect your existing (colour or mono) VGA monitor.

I suppose the fact that I'm typing this on an ELC (monochrome
Sun SPARC) "colours" my perception of what's acceptable for 

>       *  TI 34076 RAMDAC (has pixel multiplexing, 256 out of 2^16 colors).
Hmmm, I think the VGA RAMDAC's would get us where we want to go,
cheaper.  But I could easily be wrong.  Isn't this pixel multiplexing
just the "Hi-Colour" 32K colour technique?

>       *  NSC 1882 (generates Video sync, and DMA requests.?)
I'm not familiar with the NSC 1882.  Is it like the DP8520/1/2 series?

> If the peripheral controller is a 3730, then special logic would be
> provided to generate the shift register load cycles for the VRAM,
> and, of course the main CPU does the video support.

We definitely want the main R3k to be doing the video pixel bashing (dumb
frame buffer).  The feature mix on the 3730 is really hard to pass up.
> For those that don't want the video section, the motherboard could
> be sold with empty sockets for the whole video section.  A separate
> video add-on package containing the chips to plug in could be put
> together.

I'm for this, in some form.

> Video on a VESA or local bus connector:
> (I understand that VESA and local bus are the same thing; correct me
>  if I'm wrong.)

Well, you're less wrong today than in January.  There were some proprietary
implementations of a local x86 bus for video used last year, but by 
now most things called "local bus" are VESA compliant.  For our purposes
the terms are equivalent.

VESA is probably not worth the effort for a non-x86 bus.  Getting the
spec's costs money.  

Of course, on the other hand, if we could do simple, cheap video
on the m/board for folks (like me) who can't afford big-time video,
and use VESA to get a 24/32 bit 2 MByte video option for those who
want that, I'd be for it.

> Video on the ISA bus (assuming there is one):

I don't think so.  Of course, if the ISA slot is there,
and someone writes a driver, power to them.  But I wouldn't
want to rely on it for video.

> No video at all:

I don't think we can enough people interested in this configuration.

> My personal opinion is that the video should be on the motherboard as
> an option.  That is, the video designed and tested, but motherboards
> shipped with empty sockets.  I'm one of those that want the really cool
> huge colour monitors.

I can't afford a huge colour monitor.  The empty socket approach has
merits.  I would prefer "everyone gets monochrome, sockets for 8-bit
colour VRAM and RAMDAC on board".
Tim Braun                          |
Ubitrex Corporation                | Voice: 204-942-2992 ext 228
1900-155 Carlton St                | FAX:   204-942-3001
Winnipeg, Manitoba, Canada R3C 3H8 | Email: tim@ubitrex.mb.ca


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