Emerson MVME147 manual Phase

Initiator Role Custom Packet

commonly called a "thread"). The script allows the SCSI firmware to follow the TARGET bus sequences and also allows the firmware to resume a disconnected thread once a disconnect/ reselect occurs. Because the SBC allows "multithreading" of SCSI commands on the SCSI bus, a script is necessary to resume any disconnected threads. Without a script, the SCSI firmware would not have any way to check whether the TARGET performed the command that was requested through the CDB.

The following table gives the possible SCSI bus phases.

PHASE	DIRECTION	NOTES
Bus Free		No activity on the bus. SEL* and BSY* are not
		activated.
Arbitration		SCSI devices arbitrate for the use of the bus by
		activating BSY* and their ID.
(Re)Selection		One SCSI device selects another device by
		activating SEL* along with its ID and the ID for
		the other device.
Information Transfer Phases:		Command
initiator	A command
to TARGET	tells the
	TARGET
	what is
	requested by
	the initiator.
	The CDB is
	passed
	during this
	phase.
Status	TARGET	The status of a particular command is passed to
	to initiator	initiator. Examples: good, busy, check.
Data	TARGET	Data is transferred from the TARGET to the
in	to initiator	initiator as a result of a data phase requested in
		the CDB.
Data	initiator	Data is transferred from the initiator to the
out	to TARGET	TARGET as a result of a data phase requested in
		the CDB.
Message	TARGET	Messages are sent to the initiator to send bus,
in	to initiator	command, and controller information.
		Examples: command complete, save data
		pointer, restore data pointer, message reject.

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