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Re: Main CPU and Peripheral controller

To: riscy@pyramid.com
Subject: Re: Main CPU and Peripheral controller
From: jeremy@sw.oz.au (Jeremy Fitzhardinge)
Date: Mon, 5 Jul 1993 17:58:02 +1000 (EST)
Cc: riscy@pyramid.com
In-reply-to: <9307040426.AA17803@sword.eng.pyramid.com> from "Neil Russell" at Jul 3, 93 09:26:15 pm
Organization: Softway Pty Ltd
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
Neil Russell bubbles:

> In my original design, I had planned to use the IDT 79R3730 "Raster
> Image Processor".  IDT's intended market for the device is the
> Laser Printer market, however the chip lends itself to our design
> quite nicely.  In the 1992/1993 Data Book entitled "RISC Microprocessor
> Components & SubSystems", there is Advance information on the 3730.

I think this looks very good, and we should go with it.  The extra
cost doesn't seem that much considering how much it has, and how much
board space it will save.  The extra features make onboard video most
attractive, and the best solution for video.

On the subject of video:

You may of noticed that I like the onboard ideas.  Just one more point:
there has to be at least 2 frames worth of video memory for double
buffering.  Of course, you need only install one frame's worth (I
suggest), but there should be space for 2.  Using the 3730 and directly
connected video memory could get some serious graphics performance.

My Views On Other Things:

* Ether:
        Either main board or ISA.
        I don't care if ether performance is reasonable thru an ISA connector.
        Raw performace isn't the only issue:  its also important to consider
        how much CPU time it sucks while IO is happening.  If DMA can't be done
        with an ISA card, there should be some option on the main board.


* ISA:
        Yes.  This excludes the need for pretty much everything else.
        At least one slot is going to have a FDC in it.

* RAM:
        There should be memory.

* ROM:
        I don't think lots is needed.  The 3730 allows a single 8 bit
        EPROM to be used.  I think it should.  I don't see that a lot
        of stuff needs to be in it.  The limitation should be 1 chip's
        worth, so whatever EPROM with the most practial capacity.
        Having 4 EPROMs just to make a 32 bit bus would be a waste of

* RTC & misc goo:
        Well, RTC is probably best done with a Dallas Semi smart watch.
        It can go either under the EPROM or under some static ram to
        make it nv.  Other things are pretty trivial.  Serial ports are
        necessary and easy.  Parallel would be good for simple things.
        I can't see a printer port being that useful (since an ISA card
        is very cheap), but a few bits for diag LEDs is good.  You could
        have a 1 bit speaker for beeping with on it, for those who don't
        need good sound.  For those who do, it should be an option.
        No audio DACs on the board.



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