Arbitration Phase - Fujitsu MAN3184 SERIES Specifications
Disk drives scsi physical interface specifications
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Also See for MAN3184 SERIES:
- Installation manual (2 pages) ,
- Installation manual (2 pages)
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The SCSI bus enters the BUS FREE phase when the TARG stops the BSY signal in one of the
following events:
When RESET condition has been detected.
When TARG has received the following message normally.
ABORT TASK, ABORT TASK SET, CLEAR TASK SET,
LOGICAL UNIT RESET, TARG RESET, CLEAR ACA
When TARG has transmitted the following message normally.
DISCONNECT, TASK COMPLETE
When a transceiver mode change.
When the release of the SEL signal after a SELECTION or RESELECTION phase time-out.
In any case other than above, if the TARG negates the BSY signal to enter a BUS FREE phase, the
TARG informs the INIT that it has detected an ERROR condition of the SCSI bus. The TARG
can enter a BUS FREE phase forcibly regardless of ATN signal status; the INIT must treat that
phase transition as indicating the abnormal end of command. The TARG clears all hold data or
status and terminates the command being executed. It can then create sense data indicating the
detailed error condition. If the INIT detects a BUS FREE phase when it is not expected, it should
issue a REQUEST SENSE command to read the sense data.
1.6.2
ARBITRATION phase
The ARBITRATION phase allows one SCSI device to gain control of the SCSI bus. The SCSI
device that gets control of the SCSI bus can start the operation as INIT or TARG.
This is an optional system bus phase. This phase is required for the system that has two or more
INITs or uses the RESELECTION phase.
Arbitration is mandoratory and requires the detection of a Bus Free phase on the SCSI bus before
starting.
SCSI device with arbitration fairness enabled shall maintain a fairness register which records the
SCSI IDs of devices that need a chance to arbitrate. (see 1.12).
Fairness in arbitration is enabled in targets by the Disconnect-Reconnect mode page.
Figure 1.22 shows the ARBITRATION phase, and the following explains how the SCSI device
gets control of the SCSI bus.
1) The SCSI device shall wait for BUS FREE phase. (see Section 1.6.1).
2) The SCSI device shall wait at least Bus Free Delay after the BUS FREE phase detection before
driving any signal.
3) Then the SCSI device that arbitrates the bus asserts the DATA BUS bit corresponding to its
own SCSI ID and BSY signal (*1) within Bus Set Delay after the last observation of the BUS
FREE phase.
C141-E123-01EN
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