riscy
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Re: LSI chips & local bus

To: riscy@pyramid.com
Subject: Re: LSI chips & local bus
From: Andreas Busse <andy@resi.waldorf-gmbh.de>
Date: Wed, 7 Jul 93 12:18:35 +0200
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
> Large PLCC sockets usually have reliability problems with time. PLCC
> sockets rely on tension to keep the contacts together.  If they fail
> the sockets usually break in the corner and some tension is lost -
> with heat stress the contact will open and close.  Very annoying to debug.

Partially true. We use PLCC sockets in production. Yes, each 1000th
socket or so makes trouble after some time. But our products
are used "on the road". I doubt that you go on tour with your mips board :-)

> PGA sockets are better bcause they have machined pins which make better
> contact, and do not rely on tension to make contact.  Yes they are hard
> to remove - they're supposed to be.  If you have the correct tool, it is not 
> so difficult.  If we make a board with PLCC sockets, make it SMT sockets,
> so I can pull it off and SOLDER my CPU to the board!

PGA is *extremely* expensive. Nothing for our board, believe me.

> The LSI logic 33000 and 33050 are pin compatible as far as I know.

Hmm. Although this only my personal point of view, I'll tell you:
We haven't made good experience with LSI Logic. Not that their
parts don't work or the like... Their support is simply not that
good as the IDT support is.
And finally, I don't like their german salesman, but that's not
of interest.

> Also RE: local busses - I say for expansion that we should bring all
> of the CPU local bus signal to a connector(s) and make sure that the
> drivers on the PCB are tri-state or open collector.  That way for
> minimal cost those of us who want to play with fast CPU interfaces
> can.  You don't even have to stuff these extras - we who can design
> such a thing can probably solder.

Agreed. One large connector (96pin VG or the like) with all
important signals on it should be enough to add high speed
/high bandwith extensions.
But this can't be a replacement for ISA.

Andy


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