Signal States; Signal Values; Scsi Id Bits; Table 3–2 Signal Sources - Quantum DLT 8000 Product Manual

3.3

Signal States

The following paragraphs describe signal values and SCSI ID bits.

3.3.1 Signal Values

All signal values are actively driven true (low voltage). Because the signal drivers are
OR-tied, the bus terminator's bias circuitry pulls false when it is released by the drivers
at every SCSI device. If any device asserts a signal, (e.g., OR-tied signals), the signal is
true. Table 3–2 shows the ANSI-specified and defined signal sources. Any device can
assert RST at any time.
Bus Phase BSY
BUS FREE None
ARBITRATION All
SELECTION I&T
RESELECTION I&T
COMMAND Targ
DATA IN Targ
DATA OUT Targ
STATUS Targ
MESSAGE IN Targ
MESSAGE OUT Targ
All: The signal is driven by all SCSI devices that are actively arbitrating.
SCSI ID: Each SCSI device that is actively arbitrating asserts its unique SCSI ID bit. The
other seven (or fifteen) data bits are released. The parity bit DB (P or P1) can be
released or driven true, but is never driven false during this phase.
I&T: The signal is driven by the initiator, drive, or both, as specified in the SELECTION
and RESELECTION phase
Init: If driven, this signal is driven only by the active initiator.
None: The signal is released; that is, not driven by any SCSI device. The bias circuitry of
the bus terminators pulls the signal to the false state.
Winner: The signal is driven by the winning SCSI device.
Targ: If the signal is driven, it is driven only by the active 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
Table 3–2 Signal Sources
C/D I/O
SEL MSG REQ
None None
Winner None
Init None
Targ Targ
None Targ
None Targ
None Targ
None Targ
None Targ
None Targ
Quantum DLT 8000 Tape System
Signals
DB(7–0) DB(P)
ACK ATN
None None
None S ID
Init Init
Init Targ
Init Init
Init Targ
Init Init
Init Targ
Init Targ
Init Init
SCSI Description
DB(15-8) DB(P1)
None
S ID
Init
Targ
None
Targ
Init
None
None
None
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