TermPower on AlphaStation 255? - DEC

This is a discussion on TermPower on AlphaStation 255? - DEC ; 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 ...

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Thread: TermPower on AlphaStation 255?

  1. 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_

  2. Re: TermPower on AlphaStation 255?

    Ralf Folkerts wrote:
    > 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_


    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

  3. Re: TermPower on AlphaStation 255?

    Uusimäki schrieb:

    Hi Kari,

    [...]
    > 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.


    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_

  4. Re: TermPower on AlphaStation 255?

    In article ,
    Ralf Folkerts wrote:
    >
    >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" ;-)


    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
    clowenstein@ucsd.edu

  5. Re: TermPower on AlphaStation 255?

    Carl Lowenstein schrieb:

    [...]
    > 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


    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_

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