TermPower on AlphaStation 255?

Hi,

I obtained a AlphaStation 255 in order to get my Hands on OpenVMS.
During Installation there were several Problems caused by the CD-ROM not
being able to read all of my OpenVMS-CD and during problem-analysis I
checked the SCSI-Bus and found two strange things:

- The System has a IBM Hard Disk, that is jumpered to provide Term Power
(most other Systems I know get their TermPower from the Controller).

- The installed CD-ROM was jumpered to be terminated -- however, the Bus
is being terminated by a passive Terminator sitting on the last
Connector of the Cable.

My Question 1 is: Is it required for the AS255 to get Term Power from a
Device on the SCSI-Bus or is it being fed by the controller?

Question 2: Is there really a need for the SCSI-Bus to be terminated
twice (I removed the Termination-Jumper from the CD-ROM and the systems
runs 1a - but I'd like to be sure).

I didn't find this Info, so it would be great if someone could help!

Cheers,
MTIA!
_ralf_

Ralf Folkerts wrote:[color=blue]
> Hi,
>
> I obtained a AlphaStation 255 in order to get my Hands on OpenVMS.
> During Installation there were several Problems caused by the CD-ROM not
> being able to read all of my OpenVMS-CD and during problem-analysis I
> checked the SCSI-Bus and found two strange things:
>
> - The System has a IBM Hard Disk, that is jumpered to provide Term Power
> (most other Systems I know get their TermPower from the Controller).
>
> - The installed CD-ROM was jumpered to be terminated -- however, the Bus
> is being terminated by a passive Terminator sitting on the last
> Connector of the Cable.
>
> My Question 1 is: Is it required for the AS255 to get Term Power from a
> Device on the SCSI-Bus or is it being fed by the controller?
>
> Question 2: Is there really a need for the SCSI-Bus to be terminated
> twice (I removed the Termination-Jumper from the CD-ROM and the systems
> runs 1a - but I'd like to be sure).
>
> I didn't find this Info, so it would be great if someone could help!
>
> Cheers,
> MTIA!
> _ralf_[/color]

1) It depends on the setting of the controller. Normally it is enough
that just one node on the bus provides termination power. It should not
cause problems if there are others doing that as well.

2) A SCSI bus should never be terminated more than once on each end. In
this case you can terminate it with the terminator on the end of the
cable (as you probably do right now) or with removing the terminator and
plugging the last connector of the cable into the CD-ROM and having the
termination resistors and jumper connected.


Regards,

Kari

Uusimäki schrieb:

Hi Kari,

[...][color=blue]
> 1) It depends on the setting of the controller. Normally it is enough
> that just one node on the bus provides termination power. It should not
> cause problems if there are others doing that as well.
>
> 2) A SCSI bus should never be terminated more than once on each end. In
> this case you can terminate it with the terminator on the end of the
> cable (as you probably do right now) or with removing the terminator and
> plugging the last connector of the cable into the CD-ROM and having the
> termination resistors and jumper connected.[/color]

thanks for the reply! For the TermPower I was not sure if it might harm
if it's being provided by to parties. For the Termination I was sure and
removed the Termination-Jumpers from the CDROM.

Do you know how to check if the SCSI-Controller in the AS255 will
provide TermPower or not? I checked SRM but only found it's SCSI-ID,
Parity, and Disconnect but no Term-Power :-( I'd just prefer to
configure "properly" ;-)

Thanks again!
Cheers,
_ralf_

In article <kftt95-iu2.ln1@boss.home.folkerts-net.de>,
Ralf Folkerts <ralffmail-news2@yahoo.de> wrote:[color=blue]
>
>Do you know how to check if the SCSI-Controller in the AS255 will
>provide TermPower or not? I checked SRM but only found it's SCSI-ID,
>Parity, and Disconnect but no Term-Power :-( I'd just prefer to
>configure "properly" ;-)[/color]

There are SCSI terminators with LED indicators to show that TERMPWR
is present. I don't know how hard they are to find these days.

Careful exercise with a voltmeter and a pinout listing of the connector
will tell you the same thing.

carl
--
carl lowenstein marine physical lab, u.c. san diego
[email]clowenstein@ucsd.edu[/email]

Carl Lowenstein schrieb:

[...][color=blue]
> There are SCSI terminators with LED indicators to show that TERMPWR
> is present. I don't know how hard they are to find these days.
>
> Careful exercise with a voltmeter and a pinout listing of the connector
> will tell you the same thing.
>
> carl[/color]

Hi Carl,

well, I didn't think of just using a Voltmeter and check for Term-Power
on the SCSI-Bus! That's really a simple thing to check. Unfortunately I
only have some W-SCSI Terminators with LED ;-) I will check the
TermPower-Line soon :-)

Cheers,
_ralf_