🚀 go-pugleaf

Mark Ingle <mark_ingle@nospam.ifep.demon.co.uk> wrote:

> Is it acceptable to have one SCSI device on the bus switched off, and if
> so, where in the chain should it be located?

To the best of my knowledge there is no problem with this whatsoever,
it's certainly never given me any problems, put the device where you
like, I think you are suppoed to put the fastest devices closest to the
computer for speed reasons, you might actually need the device that you
expect to always be on to be at the end of the chain so that termpower
is supplied to the terminators though.

> I've tried everything I can think of... checking the device numbers, and
> selecting different numbers for different devices; moving devices on the
> chain, swapping cables.

Are you sure this is connected to having all devices on rather than a
single device?

Paul Womar <Newsmaster@pwomar.demon.co.uk> wrote:
> 
> To the best of my knowledge there is no problem with this whatsoever,
> it's certainly never given me any problems, put the device where you
> like, 

Thanks, that's exactly what I needed to hear; the external hard drive
seems to dislike the CD-R being on when booting up (even SCSI Probe
won't mount the volumes), but if it is switched on later, there are no
problems.
> 
> Are you sure this is connected to having all devices on rather than a
> single device?

I'm not quite sure what you mean; it is preferable to me to have all the
devices connected on the chain, so there isn't the business of shutting
down and swapping cables. 

Mark Ingle <mark_ingle@ifep.demon.co.uk> wrote:

> I'm not quite sure what you mean; it is preferable to me to have all the
> devices connected on the chain, so there isn't the business of shutting
> down and swapping cables. 

You seemed to imply that this only happens when ALL devices are turned
on, I'm asking you if those only happens when ALL of your devices are on
and it is not a single device that is causing the problem.

Mark Ingle wrote:
> 
> Is it acceptable to have one SCSI device on the bus switched off, and if
> so, where in the chain should it be located?
> 
> I am having problems when the devices are all switched on  . . .
SNIPPED 
> Details:
> PowerMac 7600,  System 8.0
> External bus
>  Epson Scanner*         device 2
>  SyQuest drive          device 1
>  LaCie external drive*  device 5
>  LaCie CD-R*            device 6
> 
> *These devices have switchable active termination.
> 
> Any ideas?
> 
>
This may be yet another red herring, but you indicate the presence of THRE 
devices with "switchable active termination".  If you and I think of the 
same thing when you say Active Termination, your problem may be due to 
the fact that three devices are each fighting for the opportunity to be the 
terminating device.  You really ought to only have one such device at THE 
END of the scsi chain.  If they really are active and switchable, disable the 
active termination on all but your chosen last device.  If they aren't truly 
active, merely switchable, then only have the last one in the chain 
switched on.  You could also try ALL TERMINATION SWITCHED OFF.  ( I 
have a mac LC2 which won't boot at all if its SCSI chain is terminated - 
work that one out).  If none of this helps - sorry.


 ====================/
 Stephen R Parker                  /
 steve@parkfish.demon.co.uk /
 ====================/

Thanks for all who gave suggestions.

As an update, I've tried most of these, including not using SCSI Device 5,
having devices switched on and not switched on, and changing the chain of
devices.

In summary, it turns out that the scanner is the one causing the problem
and it effectively crashes the Mac if all four SCSI devices are connected,
regardless of whether they are switched on or off*, and regardless of
whether the scanner is the last or first device in the chain. My cables
don't exceed the maximum length.

> You could also try ALL TERMINATION SWITCHED OFF.

However, if the CD-R is the last device in the chain and switched off, the
system works. As the CD-R has active termination, the chain is in effect
not terminated. Is this okay, and if not will a manual terminator properly
terminate the chain even though the device is off.

The other possible solution is moving the external hard disk to the
internal bay (internal SCSI bus) of the 7500.

> This may be yet another red herring, but you indicate the presence of THRE 
> devices with "switchable active termination". 

All the devices have a switch, and I only have the switch on the last
device in the chain.

Thanks.

Mark
mark_ingle@ifep.demon.co.uk

Steve Parker <steve@parkfish.demon.co.uk> wrote:

> You could also try ALL TERMINATION SWITCHED OFF.  ( I 
> have a mac LC2 which won't boot at all if its SCSI chain is terminated -
> work that one out).  If none of this helps - sorry.

Is there any way (via software) to see if a chain is terminated, I have
a 2 SCSI cables inside my machine and devices both inside and outside of
my machine and have no idea which part of the chain is actually the end.

Paul Womar <Newsmaster@pwomar.demon.co.uk> wrote:

> Steve Parker <steve@parkfish.demon.co.uk> wrote:
> 
> > You could also try ALL TERMINATION SWITCHED OFF.  ( I 
> > have a mac LC2 which won't boot at all if its SCSI chain is terminated -
> > work that one out).  If none of this helps - sorry.
> 
> Is there any way (via software) to see if a chain is terminated,

Not reliably.  The only way to check that I know of is to squirt a
signal into the cable and see if you get a reflection off the end.  This
needs rather specialised equipment.  The only software way of doing it
that I can think of would have to rely on detecting error rates or
something - a high error rate would imply poor termination.

> I have
> a 2 SCSI cables inside my machine and devices both inside and outside of
> my machine and have no idea which part of the chain is actually the end.

Ah...  Sorry, I'm useless.

Rowland.

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In article <19980121211931607848@ifep.demon.co.uk>,
mark_ingle@ifep.demon.co.uk (Mark Ingle) wrote:

> Paul Womar <Newsmaster@pwomar.demon.co.uk> wrote:
>
> > To the best of my knowledge there is no problem with this whatsoever,
> > it's certainly never given me any problems, put the device where you
> > like, 
> 
> Thanks, that's exactly what I needed to hear; the external hard drive
> seems to dislike the CD-R being on when booting up (even SCSI Probe
> won't mount the volumes), but if it is switched on later, there are no
> problems.

If you turn a drive on or off after your computer (the bus master)
is turned on, you may mess up the devices with active terminators.
They've assessed the position and decided if they're terminators
already -- if you then change what's turned on and what's turned
off, you'll upset them.

Always turn the computer on last and off first.  It's the bus master.

You may find that your problem goes away if you just add an external
terminator to your chain.  Active termination is always tricky.

Simon.
-- 
Simon Slavin -- Computer Contractor. | If I ran usenet, the timestamp for
   http://www.hearsay.demon.co.uk    | anything posted between 2am and 5am
 Check email address for UBE-guard.  | would *blink*. -- Nancy Lebovitz
My s/ware deletes unread >3 UBEs/day.| Junk email not welcome at this site.

Mark Ingle wrote:
> 
> Thanks for all who gave suggestions.
> 
> As an update, I've tried most of these, including not using SCSI Device 5,
> having devices switched on and not switched on, and changing the chain of
> devices.
> 
> In summary, it turns out that the scanner is the one causing the problem
> and it effectively crashes the Mac if all four SCSI devices are connected,
> regardless of whether they are switched on or off*, and regardless of
> whether the scanner is the last or first device in the chain. My cables
> don't exceed the maximum length.
> 
> > You could also try ALL TERMINATION SWITCHED OFF.
> 
> However, if the CD-R is the last device in the chain and switched off, the
> system works. As the CD-R has active termination, the chain is in effect
> not terminated. Is this okay, and if not will a manual terminator properly

SNIPPED

> All the devices have a switch, and I only have the switch on the last
> device in the chain.
> 

Another possibility for you!

At work we bought a couple of external syqyest drives a while ago and I am 
sure that as delivered, they had termination BUILT-IN.  The instructions 
told us that "if you are unable to put the unit at THE END of the SCSI chain, 
you have to partially dimantle the init to gain access to two special banks of 
terminating resistors and REMOVE them carefully".  Have a look at your 
manuals and see if any of your devices that haven't got the external 
termination ON/OFF switch, have actually got internal terminations.

If the system seems to work OK without the CD-R turned on, yet that is teh 
device with the so-called active termination set to on, it certainly sugests 
that somewhere in the chain there must be a device which is terminating.  
Identify that unit and arrange to have it at the end of teh chain, then turn 
off the CD-Rs termination.  This might sort you out.

Steve Parker

 ====================/
  Stephen R Parker                 /
 steve@parkfish.demon.co.uk /
 ====================/

In article <B0EEF678966847D34@hearsay.demon.co.uk>,
slavins@hearsay.demon.junkguard.co.uk (Simon Slavin) wrote:
> 
> Always turn the computer on last and off first.  It's the bus master.
> 
> You may find that your problem goes away if you just add an external
> terminator to your chain.  Active termination is always tricky.
> 
Thanks for that suggestion; unfortunately it doesn't make any difference.

In fact, I've now found the SyQuest drive is also affected and the
Silverlining driver mounts SQ Carts as read-only, telling me something on
the lines that the connection is unreliable. If I use the PC Exchange
driver, mounting a cart just crashes the Mac. 

I've also updated to System 8.1, but that hasn't made any difference. 

I'm waiting for some drive sleds to arrive that I ordered from Siberian
Outpost and I'll put the external drive onto the internal bus.

Mark