Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!lll-winken!unixhub!slacvm!esr
From: ESR@SLACVM.SLAC.STANFORD.EDU (Ed Russell)
Newsgroups: comp.periphs.scsi
Subject: How does it work?
Message-ID: <90325.104547ESR@SLACVM.SLAC.STANFORD.EDU>
Date: 21 Nov 90 18:45:47 GMT
Organization: Stanford Linear Accelerator Center
Lines: 23

I am a relatively new user of SCSI in my PC and would like to understand
a little more about how the device addressing works.

I recently installed a DTC 3280A "SCSI Host Adapter" in my 386-25 system.
It drives the two floppy drives in addition to the SCSI hard disk.  The
hard disk is a CDC 94211-5 (91 MB).

What I would like to understand better is how this controller, and the hard
disk, fit into the SCSI addressing scheme.  A set of dip switches on the
board is used to define the SCSI ID, values from 0-7 with a factory setting
of 7.  At boot-up, the SCSI bus is apparently interrogated and everything
sits there picking its nose for 10-20 seconds.  The boot sequence then
continues and the devices on the SCSI bus are listed:  Number 2 is the
CDC hard disk and number 7 is the Host Adapter.  I don't remember having
to set any switches or jumpers on the hard disk but it has been a while.

There are other settings on the board for setting memory address, interrupt
level, port address, etc. but I have a basic understanding of those.  I
am happy with the board and disk and they work great but I would like to
understand a little more about how this thing works in case I decide to
add additional devices to the bus later.

Post, if of potential interest to others.  Otherwise, e-mail is fine.