81-85002-01 March 2004 6-1
CHAPTER 6 SCSI Description
This chapter covers the following topics:
• “SCSI Overview” introduces the SCSI specification.
• “SCSI-2 Commands” lists the SCSI-2 commands implemented by
SDLT 220/320.
• “SCSI-3 Commands” lists the SCSI-3 commands implemented by
SDLT 220/320.
• “Parity” defines the meaning of data parity checking.
• “Signal States” defines the meaning of SCSI signal values and SCSI IDs.
• “SCSI Signals” defines SCSI signals and provides bus timing values.
6.1 SCSI Overview
The Small Computer System Interface (SCSI) is a specification for a peripheral
bus and command set that is an ANSI standard. The standard defines an I/O wide
SCSI bus that supports up to 16 devices (15 SCSI devices and one host adapter).
ANSI defines three primary objectives for SCSI-2:
1. To provide host computers with device-independence within a class of
devices.
2. To be backward-compatible with SCSI-1 devices that support bus parity and
that meet conformance level 2 of SCSI-1.
3. To move device-dependent intelligence to the SCSI-2 devices.
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