Scsi Termination; Disabling Termination; Termination Power Source; Termpwr Overview - Performance Computer PT-VME161 User Manual

SCSI Termination

The configuration shipped from PTI assumes that the PT-VME161 is at the end of the SCSI cable,
providing termination and the terminator power is provided directly from the board's +5V supply, SCSI
Termination resistor packages RP1 and RP2 are installed and Jumper K6 is set appropriately.
If the PT-VME161 does not need to terminate the SCSI cable then see "Disabling Termination" below.
You might want to review the section "Termination Power Source" if you are going to be bringing the
PT-VME161 up and down and there are other SCSI Initiators attached to the SCSIbus.
SCSI
Termination
Resistor Packs

Disabling Termination

If the PT-VME161 is not at one end of the SCSI cable then the termination will be supplied by
another SCSI device and, SCSI Termination resistor packages RP1 and RP2 (shown above) must be
removed.

Termination Power Source

The active termination circuit on the PT-VME161 draws its power from the SCSI TERMPWR
signal pin. For proper termination some device on the SCSI cable must supply +5V on the
TERMPWR line. Through jumper K6 the PT-VME161 is capable of doing this. With pins 1 and 2
of K6 shunted the power is provided to TERMPWR pin directly by the board's +5V supply. When
the pins 1 and 2 are open another device on the SCSI bus must supply TERMPWR. See
"TERMPWR Overview" below for more information.

TERMPWR Overview

There are two classes of devices on a SCS bus, Initiators and Targets. The SCSI controller on
the PT-VME161 can act as either but it typically is an initiator. Disk drives, tape drives, etc. are

Figure 6: SCSI Components

Jumper K6
Extensible Single Board Computer/Controller User's Manual 17
Performance Computer
Jumper K7
SCSI
Terminator
Fuse