Date: Mon, 27 May 2002 23:26:47 -0400 From: Mark Filipak <filipak@mrincubator.org> To: "Karel J. Bosschaart" <karelj@wop21.wop.wtb.tue.nl> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: scsi error while burning CD Message-ID: <3CF2F8F7.336D6967@mrincubator.org> References: <20020525155417.A97878@wop21.wop.wtb.tue.nl> <3CEFDA56.DA462413@mrincubator.org> <20020527132713.A2754@wop21.wop.wtb.tue.nl>
next in thread | previous in thread | raw e-mail | index | archive | help
"Karel J. Bosschaart" wrote:
>
> On Sat, May 25, 2002 at 02:39:18PM -0400, Mark Filipak wrote:
>
> > 4 - Is terminator power enabled on the SCSI controller card?
>
> Yes. This was correct for the old situation without scanner, but with
> the scanner attached it should be disabled.
No. You are confusing the terminator with terminator power. They are two
different things.
A healthy SCSI bus generally needs both terminators and terminator
power.
Terminators
===========
**Both ends** of the SCSI bus must be terminated. Since your other SCSI
devices are internal and now you are adding an external scanner, your
situation probably looks like this
Without scanner
---------------
________ _____________
/ \ / \
/__________\ _____________ \
/ | | \| | \
| | | | | | __
__=====__ __=====__ __=====_______|
| term. || | | terminator |
| enabled || | | enabled ||
| || | | ||
| || | |_ ____|
|_________||_________| |_______| |
|
SCSI drives SCSI card
With scanner
------------
________ _____________
/ \ / \
/__________\ _____________ \
/ | | \| | \
| | | | | | __ ______________
__=====__ __=====__ __=====_______| | |
| term. || | | terminator | ________ | |
| enabled || | | DISABLED || || terminator |
| || | | ||________|| enabled |
| || | |_ ____| | |
|_________||_________| |_______| | |______________|
|
SCSI drives SCSI card scanner
Whenever the scanner is *not* plugged into the SCSI bus (top picture),
you must re-enable the terminator on the SCSI card.
(If the SCSI to the scanner is 'narrower' than the SCSI supplied by the
SCSI card, then the situation gets a little more complex... see "Width
of External SCSI Bus", below.)
The terminator needs to be powered by terminator power in order to work.
Terminator Power
================
Terminator Power is voltage that is supplied by the SCSI card to power
the terminators. Most internal SCSI drives don't need terminator power
since the drives are always powered up and will supply terminator power
if the SCSI card doesn't, but an external SCSI device always needs
terminator power.
Some SCSI cards supply terminator power automatically but some require
you to set a jumper. See your SCSI card documentation.
If terminator power is *not* supplied by the SCSI card, then when you
turn the power off on the scanner its end of the SCSI bus will no longer
be terminated even though it is still connected to the external SCSI
bus. This is true regardless of whether the scanner termination is
active or passive (i.e, electonic terminator or purely resistive
terminator). So be sure that your SCSI card is configured to supply
terminator power. If your external SCSI connector is a SCSI-2, 50 pin
connector (8 data bits plus parity bit), then terminator power should be
present on pin 26. If your external SCSI connector is a SCSI-3, 68 pin
connector (16 data bits plus 2 parity bits), then terminator power
should be present on pins 17, 18, 51, and 52. I think terminator power
is always enabled for the Adaptec 2940.
Width of External SCSI Bus
==========================
You mentioned that your SCSI card is an Adaptec 2940. You failed to
mention whether it is a 2940UW, which is SCSI-3 (aka: SCSI wide, i.e.,
68 pin), which has 16 data bits. Assuming that it is, and assuming that
your scanner is SCSI-2 (i.e., 50 pin), which has 8 data bits, you will
need to enable the high byte terminator on the 2940 and disable the low
byte terminator on the 2940. Hit Ctrl-A during SCSI signon to enter the
SCSI BIOS and then configure the 2940's terminators appropriately.
Good luck -- Mark
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3CF2F8F7.336D6967>