Parallel SCSI Interface Product Manual, Rev. A ) 21
Table 5: SCSI bus data and information phase ST timing values
[1] SCSI bus timing values specified by the maximum transfer rate for the given range shall apply even if a
slower transfer rate within the given range is negotiated.
[2] Cable skew is measured at each SCSI device connection within the same bus segment with the transmit-
ted skew subtracted from the received skew.
[3] See Section 2.6 for measurement points for the timing specifications.
[4] See Section 9.6 in the ANSI SCSI Parallel Interface-5 (SPI-5) specification for examples of how to calcu-
late setup and hold timing.
Table 6: Miscellaneous SCSI bus data and information phase DT timing values
[1] SCSI bus timing values specified by the maximum transfer rate for the given range shall apply even if a
slower transfer rate within the given range is negotiated.
Timing description Reference Type
Timing values for negotiated transfer rate in
nanoseconds unless otherwise noted [1]
Asynch Fast-5 Fast-10 Fast-20 Fast-40
ATN transmit setup time
2.5.2 min 90 33 33 21.5 19.25
ATN receive setup time
2.5.3 min 45 17 17 8.5 6.75
Cable skew [2]
2.5.8 max 4.0 4.0 4.0 3.0 2.5
Receive assertion period [3]
2.5.30 min N/A 70 22 11 6.5
Receive hold time [3] [4]
2.5.31 min N/A 25 25 11.5 4.75
Receive negation period [3]
2.5.34 min N/A 70 22 11 6.5
Receive setup time [3] [4]
2.5.35 min N/A 15 15 6.5 4.75
Receive REQ(ACK) period tolerance
2.5.36 min N/A 1.1 1.1 1.1 1.1
Signal timing skew
2.5.48 max 8.0 8.0 8.0 5.0 4.5
REQ(ACK) period
2.5.41 nom N/A 200 100 50 25
Transmit assertion period [2]
2.5.55 min N/A 80 30 15 8.0
Transmit hold time [3] [4]
2.5.56 min N/A 53 33 16.5 9.25
Transmit negation period [3]
2.5.58 min N/A 80 30 15 8.0
Transmit setup time [3] [4]
2.5.59 min N/A 23 23 11.5 9.25
Transmit REQ(ACK) period tolerance
2.5.60 max N/A 1.0 1.0 1.0 1.0
Timing description Reference Type
Timing values for negotiated transfer rate in nanoseconds
unless otherwise noted [1]
Fast-10 Fast-20 Fast-40 Fast-80 Fast-160 Fast-320
Cable skew [2]
2.5.8 max 4.0 3.0 2.5 2.5 2.5 2.5
REQ(ACK) period
2.5.41 nom 200 100 50 25 12.5 6.25
Residual skew error [3]
2.5.45 max N/A N/A N/A N/A
±0.15 ± 0.20
Skew correction range [4]
2.5.49 min N/A N/A N/A N/A
±3.45 [5] ± 3.45 [5]
Signal timing skew
2.5.48 max 26.8 13.4 6.7 3.35 4.85 4.85
Strobe offset tolerance
2.5.50 max N/A N/A N/A N/A
±0.125 ±0.125
