Seagate Ultra 320 - Manual (Page 45)

Parallel SCSI Interface Product Manual, Rev. A ) 31
2.5.40 Receiver amplitude time skew
The maximum time shift of SCSI bus signals caused by the difference in receiver switching delay of a minimum
amplitude signal versus a maximum amplitude signal.
2.5.41 REQ(ACK) period
The REQ(ACK) period during synchronous transfers or paced transfers is the nominal time between adjacent
assertion edges of the REQ or ACK signal for the fastest negotiated transfer rate. For the purpose of calculat-
ing the actual REQ(ACK) period tolerance the REQ(ACK) period should be measured without interruptions
(e.g., offsets pauses). To minimize the impact of crosstalk and ISI the measurements should be made by aver-
aging the time between edges during long (i.e., greater than 512 bytes) all zeros or all ones data transfers and
by ignoring the first and last 10 transitions.
In DT DATA phases, the negotiated transfer period for data is half that of the REQ(ACK) period since data is
qualified on both the assertion and negation edges of the REQ or ACK signal. In ST DATA phases, the negoti-
ated transfer period for data is equal to the REQ(ACK) period during synchronous transfers since data is only
qualified on the assertion edge of the REQ or ACK signal.
2.5.42 Reset delay
The minimum time that the RST signal shall be continuously true before the SCSI device shall initiate a hard
reset.
2.5.43 Reset hold time
The minimum time that the RST signal is asserted. There is no maximum time.
2.5.44 Reset to selection
The recommended maximum time from after a reset condition until a SCSI target is able to respond with appro-
priate status and sense data to the TEST UNIT READY, INQUIRY, and REQUEST SENSE commands (see
SCSI Primary Commands-4 Standard).
2.5.45 Residual skew error
The maximum timing error between the deskewed data and REQ or ACK internal to the receiving SCSI device
after skew compensation.
2.5.46 Selection abort time
The maximum time that a SCSI device shall take from its most recent detection of being selected or reselected
until asserting the BSY signal in response. This timeout is required to ensure that a SCSI target port or initiator
does not assert the BSY signal after a SELECTION or RESELECTION phase has been aborted.
2.5.47 Selection timeout delay
The minimum time that a SCSI initiator port or target should wait for the assertion of the BSY signal during the
SELECTION or RESELECTION phase before starting the timeout procedure. Note that this is only a recom-
mended time period.
2.5.48 Signal timing skew
The maximum signal timing skew occurs when transferring random data and in combination with interruptions
of the REQ or ACK signal transitions (e.g., pauses caused by offsets). The signal timing skew includes cable
skew (measured with 0101...) patterns and signal distortion skew caused by random data patterns and trans-
mission line reflections as shown in ANSI standard SPI-5, T10/1525D. The receiver detection range is the part
of the signal between the “may detect” level and the “shall detect” level on either edge (see Section 8.3).
Note. For timing budget purposes the value stated in Table 6 is calculated without the benefit of skew com-