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SCSI Description

3-8 Quantum DLT 8000 Tape System

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

Signal Definition

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.

Bus Clear Delay 800 ns Maximum time for a SCSI device to stop driving all bus

signals after:

1. BUS FREE is detected.

2. SEL is received from another SCSI device during

ARBITRATION.

3. Transition of RST to true.

For condition 1, the maximum time for a SCSI device to

clear the bus is 1200 ns (1.2 µs) from BSY and SEL first

becoming both false.

If a SCSI device requires more than a bus settle delay to

detect BUS FREE, it clears the bus within a bus clear

delay minus the excess time.

Bus Free Delay 800 ns Maximum time a SCSI device waits from its detection of

BUS FREE until its assertion of BSY when going to

ARBITRATION.

Bus Set Delay 1.8 µs Maximum time for a device to assert BSY and its SCSI ID

bit on the DATA BUS after it detects BUS FREE to enter

ARBITRATION.

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Quantum DLT 8000 Manual Pagina 110