Terminating a SCSI Device

This article was previously published under Q92765
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SUMMARY
The release notes mention the importance of terminating SCSI deviceson both ends. They also mention that the Future Domain 845 and 1660cards do not have termination power. These two issues are related, butthey are not the same.

The SCSI bus must be terminated on both ends of the bus. Someone onthe SCSI bus needs to provide termination power (5V) to allow thepull-up resistors to terminate the bus properly.

The FD 845 has termination resistor packs on the card. This card doesnot place 5V on the termination power wire on the SCSI bus. Thesecards rely on the attached SCSI devices to provide 5V on thetermination pin, so your SCSI device must be configured to providetermination power. Termination power is generally supplied by all SCSIdevices, but is typically switchable. If no one on the bus providestermination power, your SCSI bus will not function correctly.

For example, to terminate the card/bus on the internal side, set yourCD-ROM to provide termination power. Leave the resistor packs in theFD. Place a terminator on the CD-ROM drive (if that is the lastdevice).
MORE INFORMATION
On SCSI adapters that have both an internal and an external connector,the "ends" of the SCSI bus are defined as follows:

  • If you have only external devices (no internal devices), one end of the bus is the last device in the external chain. The other end of the bus is the card itself. In this case, the last device in the chain must be terminated, and the resistor packs on the card itself must be in place.

    -or-
  • If you have only internal devices (no external devices), one end of the bus is the last device in the internal chain. The other end of the bus is the external connector on the adapter (or the card itself). In this case, the last device in the internal chain must be terminated. You have a choice of leaving the resistor packs on the card, or removing them and placing a SCSI terminator on the external connector.

    -or-
  • If you have both internal and external devices attached, the ends of the bus are defined as the last device in the external chain and the last device in the internal chain. In this case, the resistor packs on the card itself must be removed, and only the last device in each must be terminated.
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Article ID: 92765 - Last Review: 10/14/2013 17:58:47 - Revision: 2.1

  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • kbnosurvey kbarchive kbhardware KB92765
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