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Should we provide ISA bus support?

To: riscy@pyramid.com
Subject: Should we provide ISA bus support?
From: rei2!tsprad@uunet.UU.NET (6692)
Date: Sun, 4 Jul 1993 15:14:58 -0500 (CDT)
In-reply-to: <9307040721.AA15244@rei.com> from "UUCP Login" at Jul 4, 93 02:21:57 am
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
Neill said:
> Subject: Should we provide ISA bus support?
> No external bus at all:
> Advantages:
>       *  Very cheap
    -> Very easy to design, probably get it right the 1st time.
    -> Very little board space
> Disadvantages:
>       *  Make expansion rather difficult
    -> One would have to go back to the 'sources' and do a new board
    layout, and have new boards made
> R3000 specific high bandwidth bus (local bus?):
> Advantages:
>       *  Peripherals that we add later can go fast.
> Disadvantages:
>       *  Designing a high speed expander bus is problematical
>          (lots of wave calculations)
>       *  Connectors for high speed busses are expensive.
>       *  No cards available, unless we make them.
    -> Very difficult to design, not just the motherboard but each
    new board that you want.  No _cheap_ expansion.
> R3000 specific slow speed 8-bit bus:
> Advantages:
>       *  Cheap, small connectors
>       *  Easy to provide for on the motherboard
>       *  Simple to make cards for
> Disadvantages:
>       *  No cards available, unless we make them
    -> Cheaper and easier than a high-speed bus, but still not
> ISA bus:
> [...] the master DMA is probably the hardest to provide
> since it requires access to the main memory. 
The Adaptec 1542 is the only bus master I know of.  Motherboard DMA
obviates that one.
> The 16 to 8-bit translation is a convenience for the programmer that
> allows a 16 bit access to an 8-bit card; it can be programmed around.
> Slave DMA can be easily attached to the 3730....
What do you think of some compromise that would be compatible with
some ISA-bus boards but not others?  Or is that your point?  I
already suggested the 8-bit PC/XT bus, maybe a limited 16-bit
> How many sockets to provide?
> This is a question of how much board space we have and what others
> think.
That's all there is to say.

Ted Spradley   Recognition International, Inc.  Opinions are mine, not theirs.
2701 E Grauwyler Rd. |Your productivity is not enhanced when you're staring
Irving TX 75061      |at that thing.  Your productivity is enhanced when
214-579-6692         |the computer is working and you're doing something else.


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