ESR@SLACVM.SLAC.STANFORD.EDU (Ed Russell) (11/22/90)
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.