Quantum SDLT 320 User Manual download pdf (Page 106)

CHAPTER 6: SCSI Description SDLT 220 and SDLT 320 Product Manual

6-10 March 2004 81-85002-01

6.6.2 Signal Bus Timing

The ANSI SCSI-2 standard defines the SCSI bus timing values listed in Table 6-5.

Table 6-5. 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.

Bus Settle Delay 400 ns Minimum time to wait for the bus to settle after changing certain

control signals as called out in the protocol definitions.

Cable Skew Delay 10 ns Maximum difference in propagation time allowed between any

two SCSI bus signals measured between any two SCSI devices.

Data Release Delay 400 ns Maximum time for an initiator to release the DATA BUS signals

following the transition of the I/O signal from false to true.

Deskew Delay 45 ns Minimum time required to wait for all signals (especially data

signals) to stabilize at their correct, final value after changing.

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Quantum SDLT 320 User Manual Page 106