Terminating a SCSI Device

The release notes mention the importance of terminating SCSI devices on both ends. They also mention that the Future Domain 845 and 1660 cards do not have termination power. These two issues are related, but they are not the same.

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

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

For example, to terminate the card/bus on the internal side, set your CD-ROM to provide termination power. Leave the resistor packs in the FD. Place a terminator on the CD-ROM drive (if that is the last device).

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.