Scsi Bus Timing; Arbitration Delay; Assertion Period - Seagate ST11200 Product Manual

Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
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2.2

SCSI bus timing

Unless otherwise indicated, the delay time measurements for each SCSI device, defined in Paragraphs 2.2.1
through 2.2.14, shall be calculated from signal conditions existing at that SCSI device's own SCSI bus con-
nection. Thus, these measurements (except skew delay) can be made without considering delays in the
cable.
See Section 2.3 for Fast Synchronous transfer option timing.
Bus Phase
Bus Free
Arbitration
Selection
Reselection
Command
Data In
Data Out
Status
Message In
Message Out
ALL: The signal shall be driven by all actively arbitrating SCSI devices.
SCSI ID: A unique data bit (the SCSI ID) shall be driven by each actively arbitrating SCSI device: the other
seven data bits shall be released (i.e., not driven) by this SCSI device. The parity bit [DB(P),
DB(P1)] may be undriven or driven to the true state, but shall never be driven to the false state
during this phase.
I&T: The signal shall be driven by the initiator, target, or both, as specified in the Selection phase and
Reselection phase.
Init: If this signal is driven, it shall be driven only by the active initiator.
None: The signal shall be released; that is, not be driven by any SCSI device. The bias circuitry of the
bus terminators pulls the signal to the false state.
Winner: The signal shall be driven by the one SCSI device that wins arbitration.
Target: If the signal is driven, it shall be driven only by the active target.
2.2.1 Arbitration delay (2.4 us)
The minimum time a SCSI device shall wait from asserting BSY for arbitration until the Data Bus can be
examined to see if arbitration has been won. There is no maximum time.
2.2.2 Assertion period (90 ns)
The minimum time that a target shall assert REQ while using synchronous data transfers. Also, the minimum
time that an initiator shall assert ACK while using synchronous data transfers.
Table 2.1.4-1. Signal sources
Signals
C/D, I/O,
BSY SEL
None None
All Winner
I&T Init.
I&T Target
Target None
Target None
Target None
Target None
Target None
Target None
MSG, REQ ACK/ATN DB(7-0,P) (15-8,P1)
None None
None None
None Init.
Target Init.
Target Init.
Target Init.
Target Init.
Target Init.
Target Init.
Target Init.
None
SCSI ID
Init.
Target
Init.
Target
Init.
Target
Target
Init.
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