Scsi Considerations; Cabling; Example - Performance Computer PT-VME161 User Manual

SCSI Considerations

Cabling

The PT-VME161 SCSI interconnect is provided through the User Defined Signal pins of the VMEbus
P2 connector. The signals are organized so that a mass terminated Insulation Displacement Connectors
(IDC) can be used to attach SCSI devices to the PT-VME161. See "Table 13: VMEbus" P2" Connec-
tions" on page 77.
An interface cable can be constructed using a 50 conductor ribbon cable to attach a Eurocard (DIN 4612)
IDC with only rows A and C populated to a 50 contact ribbon cable IDC socket. The VMEbus User
Definable signals occupy 64 of the 96 positions on the P2 connector (rows A and C), however the SCSI
specification only requires 50 conductors, so pin-1 of the ribbon cable must be justified to the pin-1 end
of the Eurocard connector.
The SCSI Specification specifies that the maximum end to end length of a single-ended (TTL) SCSIbus
cannot exceed 6 meters or 19.69 ft.

Example

Following is an example cable with vendors and part numbers for the components. These configu-
rations have been tested at PTI. Figure 9 displays an example SCSI cable for the PT-VME161. The
view is with the connector sockets pointing towards you.
As long as the 6 meter maximum length identified in the SCSI specification is not exceeded there
are no constraints on the spacing between connectors other than those imposed by your physical
configuration. It is recommended that the cable be no longer than necessary for your particular appli-
cation. The SCSIbus is basically asynchronous, so long cable lengths do contribute to control signal
handshaking delays, affecting the overall performance.
VMEbus P2 Connection
Ribbon cable
SCSI device connector
64 position Insulation Displacement Connector derived from DIN 41612 type C, with rows A
and C populated (socket):
Burndy BPS3B96ACROFSZ1 or
AMP 746603-1
50 Conductor 28 AWG. Flat Cable
Spectra-Strip 843-191-2801-050 or
3M 3365/50
50 Pin Flat Cable Connector center polarized
Burndy FRS50BF-8 (strain relief included) or
Extensible Single Board Computer/Controller User's Manual 23
Performance Computer