Open SCSI Integrator's Manual for NonStop S-Series Servers

Integrating Hardware
Open SCSI Integrator’s Manual for NonStop Servers—422988-002
3-8
Specifications
Specifications
This subsection lists the specifications for external SCSI bus cables, external SCSI bus
cable connectors, SCSI port connector pinouts, and SCSI cable lengths.
External SCSI Bus Cables
An external SCSI bus cable connects an external device on a SCSI bus to the SCSI port
connector on a PMF CRU, IOMF CRU, or the S-PIC on a 6760 ServerNet/DA. These
cables are available for purchase from HP in four lengths and are listed in Table 3-2
on
page 3-10.
To ensure the reliable operation of the external device on the bus, the integrator must use
shielded cables with characteristics as specified in the Cable Requirements (Differential
Cable) subsection of the specification Information Technology - Small Computer System
Interface - 2 (ANSI X3.131 - 1994).
To ensure optimum bus operation, it is important that the external SCSI bus cable also
conform to the following three additional requirements, which supplement those given
in the SCSI-2 specification:
•
All signal cabling used for the bus must be shielded twisted-pair.
•
The characteristic impedance of the cable that connects the external device to the
bus must be in the range 115 through 160 ohms.
•
The difference in characteristic impedance between any one signal pair and another
signal pair in the cable must be no greater than 20 ohms.
External SCSI Bus Cable Connectors
The external SCSI bus cable connects the SCSI Port connector on the PMF CRU, the
IOMF CRU, or the S-PIC on the 6760 ServerNet/DA to an external SCSI device. This
connector, like its cable, must be supplied by the customer.
To ensure the reliable operation of the external device on the bus, you must use a
shielded, 68-contact, high-density connector as specified in Information
Technology - Small Computer System Interface - 2 (ANSI X3.131 - 1994).
The correct connector for the SCSI external device is a 50-contact, shielded, low-density
connector.
SCSI Port Connector Pinouts
Table 3-1 describes and identifies the signals on the pins of the SCSI port connectors on
the NonStop S-series PMF CRUs and IOMF CRUs.
The pin assignments conform to the specifications in Information Technology - Small
Computer System Interface - 2 (ANSI X3.131 - 1994).
In the two columns of Table 3-1
, differential signal pairs appear in the same row.