Quantum Instruments DLT 7000 manual Signal States, Signal Values

SCSI Description

Table 3–1 Implemented ANSI SCSI-2 Command (continued)

Command	Code	Class	Description
SPACE	11h	Mandatory	Provides a selection of positioning
			functions (both forward and backward)
			that are determined by the code and
			count.
TEST UNIT READY	00h	Mandatory	Provides a means to check if the logical
			unit is ready.
VERIFY	2Fh	Optional	Requests the drive to verify the data
			written to the medium.
WRITE	0Ah	Mandatory	Requests the drive to write the data
			transferred from the initiator to the
			medium.
WRITE BUFFER	3Bh	Optional	Used in conjunction with the READ
			BUFFER command as a diagnostic for
			testing target memory and the integrity
			of the SCSI bus.
			Used to update drive firmware from the
			host via the SCSI bus.
WRITE FILEMARKS	10h	Mandatory	Requests that the target write the
			specified number of filemarks or
			setmarks to the current position on the
			logical unit.

3.3SIGNAL STATES

The following paragraphs describe signal values and SCSI ID bits.

3.3.1 Signal Values

All signal values are actively driven true (low voltage). Because the signal drivers are OR-tied, the bus terminator’s bias circuitry pulls false when it is released by the drivers at every SCSI device. If any device asserts a signal, (e.g., OR-tied signals), the signal is true. Table 3–2 lists the ANSI-specified and defined signal sources. Any device can assert RST at any time.

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