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From: toddpw@nntp-server.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: Multi SCSI card system..
Message-ID: <1991Mar9.161552.22392@nntp-server.caltech.edu>
Date: 9 Mar 91 16:15:52 GMT
References: <13221@darkstar.ucsc.edu>
Organization: California Institute of Technology, Pasadena
Lines: 23

tmaster@ucscb.UCSC.EDU (The Master) writes:

>  I'm curious as to the safety (contention wise) of having a system with
>2 apple scsi controllers (Rev C cards) with hard drives.

> This system would be on apple ///'s, in which I have my own drivers.
>The drivers make smartport calls.  Do the cards check and handle contention
>if the scsi bus is already in use?  If not, does anyone have some
>documented code which will handle this (Since it is using device
>drivers, I can put this code in..)

I don't know about the Rev. C card, but I do know for a fact that the
DMA SCSI firmware is 100% ANSI compliant (and then some, because certain
Apple SCSI devices aren't 100% ANSI compliant) -- this includes full bus
arbitration, something the Mac still doesn't do, regardless of what Incider's
hard drive articles claim.

There's one caveat about the DMA SCSI, though: it has built in termination that
can't be removed unless you want to snip off three resistor packs and void your
nifty 1 year warranty. The Rev. C didn't have any termination of its own.

Todd Whitesel
toddpw @ tybalt.caltech.edu