Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!jarthur!uunet!zds-ux!gerry
From: gerry@zds-ux.UUCP (Gerry Gleason)
Newsgroups: comp.periphs.scsi
Subject: Re: Signals to SCSI Controller
Message-ID: <589@zds-ux.UUCP>
Date: 2 Apr 91 21:07:45 GMT
References: <13730@ccncsu.ColoState.EDU> <283400086@adaptx1>
Reply-To: gerry@zds-ux.UUCP (Gerry Gleason)
Organization: Zenith Data Systems
Lines: 18

In article <283400086@adaptx1> neese@adaptx1.UUCP writes:

>>/* ---------- "Signals to SCSI Controller" ---------- */
>>I would like to know if an SCSI controller uses the IRQ, DACK, and DRQ lines
>>to the computer.  Please forgive me if this is "Common Knowledge" in this
>>group (I just joined 2 days ago).

>Depends on the SCSI adapter.  IRQ would certainly be used by all, but the
>DACK/DRQ lines are only used for DMA.  Bus masters would use these signals,
>but PIO cards would not.

Correct me if I'm wrong, but bus masters would not use these signals, but
would use "Bus Request" and "Bus Acknowledge" lines (whatever they are
called on the bus).  The DACK/DRQ lines are for "native" DMA, that is
DMA managed by DMA chips on the system board.  Note that this type of
DMA is pretty slow, slower than what is possible with bus master DMA.

Gerry Gleason