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5-2 A-61124 March 1999
SCSI interface signal
lines
The SCSI interface uses 18 signal lines:
Select (SEL)
Acknowledge (ACK)
Attention (ATN)
Reset (RST)
Target
Busy (BSY)
Data (DB(0)-DB(7))
Data Parity (DB(P))
Control/Data (C/D)
Input/Output (I/O)
Message (MSG)
Request (REQ)
Host
Computer
Initiator
Issuing SCSI
commands
There are seven steps or phases for issuing commands to the
scanner or controller:
Bus Free
Arbitration
Selection
Command
Data
Status
Message
Bus Free phase — the SCSI bus is not being used by an initiator
(host computer) or the target (scanner). No signals on the bus
are asserted.