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SCSI Description

3-6 Quantum DLT 4000 Tape Drive

3.3.2 SCSI ID Bits

SCSI permits a maximum of eight SCSI devices on a SCSI bus (16 devices are

permitted when using wide SCSI). Each SCSI device has a unique SCSI ID

assigned to it. This SCSI ID provides an address for identifying the device on the

bus. On the drive, the SCSI ID is assigned by configuring jumpers or connecting

remote switches to the option connector. Chapter 2, Hardware Implementation

has full instructions for setting the SCSI ID.

3.4 SCSI SIGNALS

The following paragraphs define SCSI signals and bus timing values.

3.4.1 SCSI Signal Definitions

Table 3–3 defines the SCSI bus signals.

Table 3–3 SCSI-2 Bus Signal Definitions

Signal Definition

ACK

(acknowledge)

A signal driven by the initiator as an acknowledgment of receipt of

data from a target or as a signal to a target indicating when the target

should read the data (out) lines.

ATN (attention) A signal driven by an initiator to indicate that it has a message to send.

BSY (busy) An OR-tied signal that indicates that the bus is in use.

C/D

(control/data)

A signal driven by a target that indicates whether CONTROL or DATA

information is on the DATA BUS. True (low voltage) indicates

CONTROL.

DB(7–0,P)

(data bus)

Eight data-bit signals, plus a parity-bit signal that form a DATA BUS.

DB(7) is the most significant bit and has the highest priority (8 or 16-

bit) during ARBITRATION. Bit number, significance, and priority

decrease downward to DB(0). A data bit is defined as 1 when the

signal value is true (low voltage) and 0 when the signal value is false

(high voltage). Data parity DB(P) is odd. Parity is undefined during

ARBITRATION.

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Quantum DLT 4000 Handbuch Seite 68