Quantum 10K II - Manual (Page 332)

Appendix B. SCSI Bus Signal Timing
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives B–11
B.4 SCSI Signals
Table B-7 defines the SCSI-3 bus signals.
Table B–7 SCSI–3 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.
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.