#SCSI Unit Nos.
14 messages in this thread
I'm looking for some help with SCSI drives.
I have 2 hard drives and a CDRom in my A2000 attatched to an A2091 card.
The cable runs from the card to the boot disk (unit 6) to the next hard
drive (unit 3) and on to the CD (unit 2). Where should the terminator
resistors be? right now they are on the boot drive (unit 6). Am I
correct?
Any help or explanation will be appreciated.
David Kay
Flying in from Montreal.
The last drive on the chain (in your case, the CD) and no others should be
terminated.
Dale L. Larson Intangible Assets Manufacturing (info@iam.com)
"That's the best part about being crazy. You see things no one else can see."
Dale:
>The last drive in the chain…and no others should be terminated.
A clarification and possible exception: I have an A2091 like David, and I
run three internal SCSI devices on it (including a floptical and two hard
drives, one being the Quantum that came with the controller card). Oddly,
these devices seem to work fine whether I terminate only the last drive or
also terminate either of the other two drives.
Now I've tried adding one of those el cheapo Creative Computer NEC-25
MediaVision external CD-ROM drives to the 25-pin external SCSI port on the
A2091. The Commodore manual says in a situation like this both last drives
(on the external and internal loops) should be terminated. Creative
supplied a cable in-line terminator which is essential to get any kind of
rise out of the CD-ROM.
So far, however, even though other purchasers report getting the NEC-25 up
and running, I've failed, no matter what termination scheme I've tried
(still have a few more to run through, though). The CD-ROM is noticed by
HDToolbox or AsimCDFS and an icon goes up on the Workbench, but mounting a
disc at best causes it to spin endlessly with the "busy" light on, while
the rest of my system slows to a crawl. Pop the disc and the system
reverts to its normal speed.
Obviously, I haven't hit on the magic combo of termination yet. Maybe
something in my system is not friendly to the CD-ROM (possible, the
floptical drive).
— RON LEGRO / Milwaukee via Autopilot 1.73
"Accept nothing less than a high standard of standardness."
You have to pull termination from your A2091 before you terminate an
internal and an external device.
Dale L. Larson Intangible Assets Manufacturing (info@iam.com)
"That's the best part about being crazy. You see things no one else can see."
>You have to pull termination from your A2091 before you terminate an
>internal and an external device.
Been there. Done that. No joy.
There aren't terminators on the controller itself in addition to the
Quantum drive that came with the A2091, are there? The manual and visual
inspection suggest not.
— RON LEGRO / Milwaukee via Autopilot 1.73
"Accept nothing less than a high standard of standardness."
What in the manual suggests that there is no termination on the A2091?
How do you suggest that you terminate both ends of an internal-only bus
without an external terminator (which no one uses on A2091s)?
I'm willing to bet a fair sum that the A2091 has terminators on the board.
I believe they are right next to the 50-pin connector, but they probably
aren't socketed. If you have only a drive mounted to the card and an
external chain which is terminated, terminating only the card and the
external chain will probably work. If you have a real chain inside and a
real chain outside, reliability is going to dictate that you remove the
terminators and that you terminate the last internal drive and the last
external drive.
Other configurations might happen to work, but may be slower and more
error prone and may lead to unexplainable problems at some future date.
Dale L. Larson Intangible Assets Manufacturing (info@iam.com)
"That's the best part about being crazy. You see things no one else can see."
A plea for help. Does anyone know where I can get a newer version of "hddisk",
the device driver for a Commodore 2090A (not 2091) SCSI controller? The version
I have does not support SCSI direct commands nor does it work with the HD tool.
Also – anyone have report on if the 2090 can handle an external tape drive?
Maybe I should find a 2091 or some other card and driver? —- Would appreciate
an e-mail reply, on CIS or, better yet, to
childress_steve@msmail.iipo.gtegsc.com
thanks.
What you say makes sense, except for the following line, which has an
ambiguous phrase which I've marked with asterisks:
>If you have a real chain inside and a real chain outside, reliability is
>going to dictate that you *remove the terminators* and that you terminate
>the last internal drive and the last external drive.
I presume that in the above you weren't referring to removing the A2091
on-board terminators you postulated, but rather the terminators on all but
the last devices. I realize the controller is itself a device but I don't
think you meant that.
>What in the manual suggest that there is no termination on the A2091?
The absence of any reference. The manual goes so far as to diagram the
terminators on the supplied Quantum drive aboard the controller and
discusses them in detail, but makes no reference whatever to any separate
controller termination. It provides a diagram of the A2091 card
identifying various jumpers and connectors but is silent on termination.
Also, someone else had mentioned in another post to me that controllers
per se aren't terminated. I'll look and see if I can find any
terminator-type devices near the connector; not that such knowledge will
be of much use, if I do find them and they're soldered in,
Being forced to delve into this subject suddenly has me thinking other
dangerous thoughts. e.g., the possible use of Logical Unit Numbers. From
what I can gather, while each drive obviously must have a different
physical address you apparently could have devices sharing a physical
address but having different LUNs — perhaps for a removeable hard drive.
Or at least that's what I glean from what little I've read on the subject.
Anyway, thanks for trying to help me sort this out. Will keep on plugging;
trial and error is usually my style when it comes to this kind of
challenge.
Ron,
LUN's are additions to SCSI ID's. You can have a LUN of 0 to 7 just
like you can have SCSI ID's of 0 to 7. Since the host adapter always has a LUN
of 0 and no other device should share that SCSI ID, then in theory.. for the
other 7 SCSI ID's, you could have 8 devices each for a total of 56 devices
attached to a single SCSI bus.
In practice…that'd be foolish, along with the fact that 'consumer'
SCSI devices typically don't have jumpers to set the LUN, they're hard wired at
0, or at best a single jumper to allow a LUN of 0 or 1.
From my experience…a typical device that uses LUN's would be a bridge
controller that converts one type of interface to another. For example, on
some of our UNIX mini's here at work, we have multiple ESDI drives attached to
a single ESDI-SCSI bridge controller with each drive tap on the bridge (there
are 4 taps on the bridge controller) having a different LUN, but the bridge
only taking up one SCSI ID. It's a rare day when you find a single drive with
a LUN jumper.
Don
Don,
I work for Canon and when linking our colour copiers to PC's/Mac's, our
interface (which is SCSI) has two LUN's; One for the scanner of the copier
and one for the printer. We have no way to adjust these at all, they're
hard wired.
Kevin
Flying AutoPilot from Surry in the UK
Yeah, I mean't remove the terminators from the A2091.
As to the manuals, since when were C= manuals a model of perfection? 🙂
I took a quick look at a 2091 the other day, and it sure looked like there
were terminating resistors soldered onto the board right next to the
50-pin connector.
Dale L. Larson Intangible Assets Manufacturing (info@iam.com)
"That's the best part about being crazy. You see things no one else can see."
Ron,
I vaguely recollect the beginning of this thread as centering around the
use of a Nec CD25. If so, look no further. It's this drive. I could get it
to work reliably with my 500xp but never on my 3000. I guess the Supra
isn't as sensitive about termination. I fussed around it with Amax on my
3000 and Mac Scsi software could find the drive out there, but always
claimed it was unterminated, even with in line termination.
-Richard
Ron:
<<A clarification and possible exception: I have an A2091 like David, and I
run three internal SCSI devices on it (including a floptical and two hard
drives, one being the Quantum that came with the controller card). Oddly,
these devices seem to work fine whether I terminate only the last drive or
also terminate either of the other two drives.>>
Sometimes you can get away with putting termination all over the SCSI buss or
chain. However, you sinking more of the buss power than you need to. In some
cases the buss can supply the power of the additional terminations. However,
the best policy is to have only two terminators one on the card (a SCSI device)
and one on the end of the internal or external drive chain. If you have an
external and internal drive chain then you should only have two terminators:
none on the card, but one at the end of each drive chain (or should I say SCSI
chain as you might have a scanner with a SCSI connection). If your system is
configured this way then your problem is not SCSI termination.
Good Luck!
Norm