Quantum Instruments DLT 7000 Signal Bus Timing, Scsi Description SCSI-2 Bus Signal Definitions

SCSI Description

Table 3–3 SCSI-2 Bus Signal Definitions (continued)

Signal	Definition
I/O (input/output)	A signal driven by a target that controls the direction of data
	movement on the DATA BUS with respect to an initiator. True
	indicates input to the initiator.
	Also used to distinguish between SELECTION and RESELECTION
	modes.
MSG (message)	A signal driven by a target during the MESSAGE phase.
REQ (request)	A signal driven by a target to indicate a request for an
	information transfer to or from the initiator. Each byte of data
	transferred is accompanied with a REQ/ACK “handshake”. See
	also, ACK.
RST (reset)	An OR-tied signal that initiates a RESET condition.
SEL (select)	An OR-tied signal used by an initiator to select a target or by a
	target to reselect an initiator.

3.4.2 Signal Bus Timing

The ANSI SCSI-2 standard defines the SCSI bus timing values shown in Table 3–4.

Table 3–4 SCSI Bus Timing Values

Timing Description	Value	Description
Arbitration Delay	2.4 µs	Minimum time a SCSI device waits from asserting BSY
		for arbitration until the DATA BUS can be examined to
		see if arbitration has been won; there is no maximum
		time.
Assertion Period	90 ns	Minimum time a drive asserts REQ while using
		synchronous data transfers; also, the minimum time
		that an initiator asserts ACK while using synchronous
		data transfers.

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