A.3 Bus Phases
Appendix A-11
A.3.1
BUS FREE phase
The BUS FREE phase is used to indicate that no SCSI device is actively using the SCSI bus, and
that it is available.
SCSI devices shall detect the BUS FREE phase after the SEL and BSY signals are both false for at
least a bus settle delay.
SCSI devices shall release all SCSI bus signals within a bus clear delay after the BSY and SEL
signals become continuously false for a bus settle delay.
A.3.2
ARBITRATION phase
The
ARBITRATION phase allows one SCSI device to gain control of the SCSI bus so that it can
initiate or resume an I/O process. The procedure for an SCSI device
to obtain control of the SCSI
bus is as follows:
1)
The SCSI device shall first wait for the BUS FREE phase to occur.
2)
The SCSI device shall wait a minimum of a bus free delay after detection of the BUS FREE phase (i.e.
after the BSY and SEL signals are both false for a bus settle delay) before driving any signal.
3)
Following the bus free delay in Step 2), the SCSI device may arbitrate for the SCSI bus by asserting
both the BSY signal and its own SCSI ID, however, the SCSI device shall not arbitrate (i.e. assert the
BSY signal and its SCSI ID) if more than a bus set delay has passed since the BUS FREE phase was last
observed.
4)
After waiting at least an arbitration delay (measured from its assertion) 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 device has lost the arbitration and the SCSI device may release its signals and return to Step
1). If no higher priority SCSI ID bit is true on the DATA BUS, then the SCSI device has won the
arbitration 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 1).
5)
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
.
bus clear delay
bus settle delay
BSY
SEL
others
BUS FREE phase
Summary of Contents for M3097DG
Page 1: ...C150 E103 01EN M3097DG Image Scanner OEM Manual ...
Page 2: ......
Page 4: ...This page is intentionally left blank ...
Page 44: ...3 3 Optional image function 3 23 ...
Page 67: ...5 4 Consumable 5 13 Two rollers are included Figure 5 4 Pick roller ...
Page 70: ...6 3 Figure 6 1 Jam clearance ...