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SCSI Description

Quantum DLT 4000 Tape Drive 3-7

Table 3–3 SCSI-2 Bus Signal Definitions (continued)

Signal Definition

DB(15–8,P1)

(data bus)

Eight data-bit signals, plus one parity-bit signal, that forms an

extension to the DATA BUS. They are used for 16-bit (wide) interfaces.

DB(15) is the most significant bit and has the higher priority (but

below bit DB(0) during ARBITRATION. Bit number, significance, and

priority decrease downward to DB(8). Data Parity DB (P1) is odd.

I/O

(input/output)

A signal driven by a target that controls the direction of data

movement on the DATA BUS with respect to an initiator. True indicates

input to the initiator.

Also used to distinguish between SELECTION and RESELECTION modes.

MSG (message) A signal driven by a target during the MESSAGE phase.

REQ (request) A signal driven by a target to indicate a request for an information

transfer to or from the initiator. Each byte of data transferred is

accompanied with a REQ/ACK “handshake”. See also, ACK.

RST (reset)

An OR-tied signal that initiates a RESET condition.

SEL (select)

An OR-tied signal used by an initiator to select a target or by a target to

reselect an initiator.

3.4.2 Signal Bus Timing

The ANSI SCSI-2 standard defines the SCSI bus timing values shown in Table

3–4.

1 2 ... 64 65 66 67 68 69 70 71 72 73 74 ... 299 300

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Quantum DLT 4000 Handbuch Seite 69