Special Signals; Differential Sense; Terminator Power; Table 2-2 Scsi Device Types Into Scsi Bus Types - Sun Microsystems storagetek sl500 Reference Manual

Special Signals

The library supports two special SCSI bus signals:
Differential Sense (DIFFSENS)
■
Terminator Power (TERMPWR)
■

Differential Sense

The differential sense (DIFFSENS) is a DC voltage level that distinguishes among
the two SCSI alternatives: single-ended, and LVD:
Single-ended:
LVD:
The DIFFSENS signal helps prevent damage to the SCSI bus and other equipment
when the SCSI device is incompatible with the SCSI bus. Some potential for device
damage still exists, however, depending on the type of incompatibility. The
following table

TABLE 2-2 SCSI Device Types into SCSI Bus Types

If you plug this device type
into this SCSI bus type . . .
Single-ended (SE) device
LVD device

Terminator Power

The library is capable of providing terminator power on the SCSI bus. All devices
supporting the differential alternative (LVD) must have the ability to provide
terminator power (TERMPWR) with the following characteristics:
Note – Industry standards dictate that no more than three devices should provide
terminator power on the bus. This ensures that voltage on the bus stays high (+5
VDC) without over-driving the signal or overloading the bus.
Jumpers on the library enable terminator power.
96122 • Revision: F
-0.35 V to +0.5 V
+0.7 V to +1.9 V
(TABLE 2-2) shows the effects of different types of incompatibility.
Single-Ended (SE) Bus
No effect.
This is a proper connection.
The LVD device will run in
SE mode.
LVD Bus
The entire bus will run in SE
mode (with SE restrictions).
No effect.
This is a proper connection.
Chapter 2 SCSI Bus Physical Description 11
Special Signals