d)After waiting at least an arbitration delay (measured from its assertion of the BSY signal) the SCSI device shall examine the DATA BUS. If a higher priority SCSI ID bit is true on the DATA BUS (DB(7) is the highest), then the SCSI devices has lost the arbitration and the SCSI device may release its signals
and return to Step(a). If no higher priority SCSI ID bit is true on
the DATA BUS, then the SCSI device has won the arbitration INTERFACE and it shall assert the SEL signal. Any SCSI device other than the winner has lost the arbitration and shall release the BSY signal
and its SCSI ID bit within a bus clear delay after the SEL signal becomes true. An SCSI device that loses arbitration may return to Step(a).
e)The SCSI device that wins arbitration shall wait at least a bus clear delay plus a bus settle delay after asserting the SEL signal before changing any signals.
SELECTION PhaseThe SELECTION phase allows an initiator to select a target for the purpose of initiating some target function (e.g., READ or WRITE command). During the SELECTION phase the I/O signal is negated so that this phase can be distinguished from the RESELECTION phase.
The SCSI device that won the arbitration has both the BSY and SEL signals asserted and has delayed at least a bus clear delay plus a bus settle delay before ending the ARBITRATION phase. The SCSI device that won the arbitration becomes an initator by not asserting the I/O signal.
The initiator shall set the DATA BUS to a value which is the OR of its SCSI ID bit and the target’s SCSI ID bit and it shall assert the ATN signal (indicating that a MESSAGE OUT phase is to follow the SELECTION phase). The initiator shall the wait at least two deskew delays and release the BSY signal. The initiator shall then wait at least a bus settle delay before looking for a response from the target.
The target shall not respond to selection if bad parity is detected. Also, if more than two SCSI ID bits are on the DATA BUS, the target shall not respond to selection.
M3099GX/GH OEM Manual |