Ultra Scsi; Outline; Device Connection - Fujitsu MAW3073 SERIES Specifications

When two buses having the different width are interconnected, the DATA BUS signal of the bus
having a larger width shall be terminated with an adapter. The connector has been designed to
electrically isolate the A and P shielded connectors from each other.
Two reserved lines (having A-cable contact numbers 23 and 24) and the open lines (having A-
cable contact number 25) on the A cable are the TERMPWR lines (having the P-cable contact
numbers 33, 34 and 35) on the P cable.
An eight-bit device connected to the single-ended P-cable shall keep open nine signals of DB(8 to
15) and DB(P1).
An eight-bit device connected to the low voltage differential P-cable shall keep open 18 signals of
+DB(15 to 8), -DB(15 to 8), +DB(P1) and -DB(P1).
1.11

Ultra SCSI

1.11.1

Outline

The SCSI-3, Fast-20 Standard defines the characteristics of cables, signals, and transceivers
required for 20 MB/s signal transmission. The services required to communicate with a higher
layer protocol is defined by the SCSI-3 Parallel Interface Standard.
In addition, the expansion to SCSI-3 parallel interface is defined to enhance the available data
transfer rate. Only the interface specifications associated with the higher data speed are included
in this Standard.
1.11.2

Device connection

Connection between an single-ended transceiver and device
The maximum length of accumulated signal path between terminators shall be 3.0 m if up to four 25-pF
capacitance devices are used. The maximum length of accumulated signal path between terminators
shall be 1.5 m if five to eight devices that have maximum capacitance are used. When connecting nine or
more devices, the specifications exceeding the minimum value defined in this manual shall be controlled.
The distance between devices should be equal to each other, and the last device should locate close to the
terminator as much as possible.
If the all bus elements (including cable, device interface, ambient noise, and other parameters) are
controlled well to realize an environment better than the minimum required conditions, the path
may be extended and more devices may be connected (see Section 1.11.3 "Single-ended I/O
characteristics").
The signal path shall have the following impedance characteristics.
1) 90 +/-6 Ω for REQ and ACK signals
2) 90 +/-10 Ω for all other signals
The stub length shall not exceed 0.1 m. It shall be measured from the transceiver position toward
the connection point of trunk SCSI bus. The space between devices on the trunk SCSI bus shall be
at least three times larger than the stub length to prevent clustered stubs.
C141-C011 1-129