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).

iThe Target stands by in the Bus Free Phase until the Initiator selects it.

iiWhen 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.

iiiWhen 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.

ivThe 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.

vThe 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