Bus Signals; Table 3-2 Bus Signals - Sun Microsystems storagetek sl500 Reference Manual

Bus Signals

Bus Signals
Communication between two devices on the SCSI bus occurs any time after they
establish connection using the bus phases. When two devices communicate, one
device acts as an initiator and the other device acts as a target.
FIGURE 3-2

TABLE 3-2 Bus Signals

BSY
SEL
C/D
I/O
MSG
REQ
ACK
ATN
RST
DB(0-n)
DB(P,P1)
FIGURE 3-2 Signal Source and Direction
INITIATOR
18 SL500: Interface Reference Manual • July 2008
shows the source and direction of the SCSI bus signals.
Busy is a control signal that indicates the SCSI bus is in use.
Select is a control signal that selects a target or initiator.
Control and Data signals are driven by the target to indicate whether
control or data information is being transferred.
Input and Output are control signals driven by the target to control the
direction data travels on the bus (with respect to the initiator).
Message is a control signal driven by the target.
Request is a control signal driven by the target to indicate a request for a
REQ/ACK data transfer handshake.
Acknowledge is a control signal driven by an initiator to indicate an
acknowledgment for a REQ/ACK data transfer handshake.
Attention is a control signal driven by an initiator to indicate an Attention
condition.
Reset is a control signal that generates a Reset condition when asserted.
Data bus signals (0-n) transfer data where n indicates the number of data
bus signals.
Data bus parity signals (P,P1) are undefined during the Arbitration phase
and are defined as odd parity during data transfer.
BSY
SEL
C/D
I/O
MSG
REQ
ACK
ATN
RST
DB (0-n) DB (P,P1)
TARGET
Revision: F • 96122