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OCTOBER 2006 VXA-320 TAPE DRIVE
37
COMMUNICATION INTERFACE VERSUS COMMAND PROTOCOL
6
COMMUNICATION INTERFACE
AND COMMAND PROTOCOL
This chapter provides an overview of the communication interface and
command protocol used by the VXA-320 (VXA-3) tape drive. It includes the
following topics:
Communication interface versus command protocol
SCSI communication interface
SCSI interface requirements
SCSI command protocol
COMMUNICATION INTERFACE VERSUS COMMAND PROTOCOL
When a device is connected to a host computer, their interaction is
accomplished via a communication interface (for example, a parallel SCSI bus).
The communication interface is comprised of the physical interface (for
example, cables, connectors, and control circuitry) and the signaling protocol
used during communication.
The physical interface determines the number of devices that can be attached
to a bus or network loop, the maximum length of the cables, and the physical
characteristics of the cable itself (for example, the number of wires, shielding,
and so forth). The signaling protocol defines the electrical characteristics and
timing of signals carried by the cable, the message system requirements,
transmission speeds and maximum data transfer rates, as well as the encoding
and decoding of the individual bit patterns representing commands passing
between the individual devices.