OEM MANUAL:K6602924
3 SCSI BUS
Revision: 1 / Date: 2003.03.06
Page: 31 / 273
3
SCSI BUS
This chapter describes the SCSI bus interface that is common to all SCSI controller
commands. Refer to the appropriate specifications or documents for the physical
specifications, SCSI bus signal definitions, bus phases, and bus signal timings of the
SCSI bus.
3.1
SCSI BUS FUNCTIONS
3.1.1 COMMAND RECEPTION
This SCSI controller can receive commands from a maximum of 7 (15 for Wide
SCSI ) host computers (initiators).
When the controller receives a new command while executing or enqueuing a
previous command from the same host computer, it informs the ''Busy'' status to
the new command, except during Tagged Queuing.
3.1.2 COMMAND QUEUING
(1) Untagged Queuing
The controller can enqueue one command for each host computer when it cannot
execute the received command immediately (there is already an enqueued or
executing command).
The controller, however, does not enqueue the received command and reports the
Busy status in the following cases:
· The controller cannot disconnect from the SCSI bus after receiving the CDB,
that is, bit 6 of the Identify message is set to 0 (the host computer does not
support disconnect or reconnect function) or the Disconnect message from the
controller is rejected.
The controller executes the queued commands with the FCFS (First Come First
Served) algorithm.