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Page 8 DDS-4 SCSI Interface Manual, Rev. B

Figure 2-1

Phase Sequencing with Arbitration

RESET CONDITION

BUS FREE

PHASE

ARBITRATION

PHASE

SELECTION OR

RESELECTION

PHASE

COMMAND,

DATA, STATUS,

OR MESSAGE

PHASE

Arbitration is won by the highest priority SCSI device when both BSY and SEL are

asserted and a delay of at least 1200 nSec (1 bus clear delay + 1 bus settle delay)

occurs before the Arbitration Phase ends and the Selection Phase begins. Signal

timing is shown in Figure 2-3 and the complete Arbitration Phase protocol is

summarized in the following table.

Figure 2-2

Arbitration and Selection Phase Signal Timing

Step Procedure

The SCSI device first waits for a Bus Free Phase to occur. The Bus

Free Phase is detected when both the BSY and SEL signals are

simultaneously and continuously false for a minimum of a bus settle

delay of 400 nSec.

1 2 ... 15 16 17 18 19 20 21 22 23 24 25 ... 180 181

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