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SCSI Operation Procedure
This section explains the operational procedures for the SCSI.
For details concerning SCSI specifications for individual
operations, refer to ANSI X3.131-1986 ‘‘Small Computer System
Interface.’’
Communication Operation
The following procedure is used to transfer data between the
scanner (Target) and a host computer (Initiator).
i The Target stands by in the Bus Free Phase until the Initiator
selects it.
ii When selected by the Initiator, the Target checks for ATN on the
SCSI bus line. If active low (L), the Target changes to the
Message Out Phase; the Initiator then sends a 1-byte
message to the Target. The Target must receive the Identify
message at this point. If the Target receives the Identify
message or the Bus Device Reset message, the Target
changes to the Message In Phase and sends the Message
Reject message.
iii When selected during a carriage reset, the scanner sends a
BUSY status message and then advances to item x. When the
scanner is in a fatal error state, it creates an error code and
sense data and then advances to item ix.
iv The Target changes to the Command Phase and receives a
command (6-byte command of group 0). The target then
checks the Link Flag bits in the command. If both are not ’0’,
an error will occur, the Target creates an error code and sense
data and then advances to item ix.
v The Target checks the command. When the command operation
code is Request Sense or Inquiry and there is no error in the
other parameters, the command is executed. If there is a
parameter error, however, the Target creates an error code
and sense data and then advances to item ix.
Interface Specifications A-13