Quantum 10K II - Manual (Page 330)

Appendix B. SCSI Bus Signal Timing
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives B–9
B.3 Signal States
The following paragraphs describe the SCSI signal values and SCSI ID bits.
B.3.1 Signal Values
All signal values are actively driven true (low voltage). Because the signal drivers
are OR-tied, the bias circuitry on the bus terminator 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 B-5 shows the ANSI-specified and defined signal
sources. Any device can assert RST at any time.
Table B–5 Signal Sources
SIGNALS
C/D
I/O
Bus Phase MSG ACK DB(7–0) DB(16-8)
BSY SEL REQ ATN DB(P) DB(P1)
BUS FREE None None None None None None
ARBITRATION All Winner None None S ID S ID
SELECTION I&T Init None Init Init Init
RESELECTION I&T Targ Targ Init Targ Targ
COMMAND Targ None Targ Init Init None
DATA IN Targ None Targ Init Targ Targ
DATA OUT Targ None Targ Init Init Init
STATUS Targ None Targ Init Targ None
MESSAGE IN Targ None Targ Init Targ None
MESSAGE OUT Targ None Targ Init Init None
All: The signal is driven by all SCSI devices that are actively arbitrating.
S 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 DB (P1), can be
released or driven true, but is never driven false during this phase.
I&T: The signal is driven by the initiator, target (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.