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C-30 Sun Ultra 60 Service Manual • August 2001
C.1.14 SCSI
The system unit implements a small computer system interface (SCSI) Fast-20
(UltraSCSI) parallel interface bus. The UltraSCSI provides the following:
■ Efficient peer-to-peer I/O bus devices.
■ Mechanical, electrical, and timing specification definition that support transfer
rates of 20 or 40 Mbytes per second (corresponding to the data path width of
an 8-bit, or 16-bit bus, respectively).
■ Peak bandwidth of 40 Mbytes per second (with implemented 16-bit bus width).
The internal SCSI bus is terminated at each end. One set of terminators is located
close to the CD-ROM drive connector on the CD-ROM SCSI card. A second set of
terminators is located close to the 68-pin external SCSI connector.
FIGURE C-10 shows
the SCSI bus configuration.
FIGURE C-10 Configuration for the SCSI Bus
C.1.14.1 Host Adapter
The host adapter is a Symbios Logic PCI-SCSI I/O processor IC. The host adapter
and all target devices comply with the Fast-20 single-ended drivers and receivers
characteristics. The electrical characteristics of the output buffers include:
■ V
ol
(output low) equals 0 to 0.5 Vdc with Iol at 48 mA (signal asserted)
■ V
oh
(out high) equals 2.5 to 3.7 Vdc (signal negated)
■ t
rise
(rising slew rate) equals 520 mV per nanosecond maximum
(0.7 to 2.3 Vdc)
■ t
fall
(falling slew rate) equals 520 mV per nanosecond maximum
(2.3 to 0.7 Vdc)
CD-ROM
Internal SCSI bus
drive
(8-bit)
Disk 1
(UltraSCSI)
Disk 0
(UltraSCSI)
Host
adapter
(UltraSCSI)
External
devices
(UltraSCSI)
SCSI bus
External to chassis
T
T
T
SCSI bus