Quantum DLTtape DLT 4000, Product Manual

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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.