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Information Transfer Phases SDLT 600 SCSI Interface Guide

2-2 January 2005 81-81200-02 REV A01

2.2 Information Transfer Phases

The COMMAND, DATA, STATUS, and MESSAGE phases are known as the information transfer

phases because they are used to transfer data or control information. Keep the following guidelines in

mind:

• SDLT tape drives support wide asynchronous and synchronous data transfers.

• Odd parity is generated during all information transfer phases during which the device writes data

to the SCSI bus and parity is checked during all transfer phases in which data is read from the bus

by the SDLT tape drive.

• SDLT tape drives support block sizes from 4 bytes to 16,777,212 bytes.

• The tape drive disconnects from the SCSI bus at regular intervals during information transfer

phases to allow other devices to access the bus. These disconnects are user-configurable using the

Disconnect-Reconnect Page of the MODE SELECT command.

• The SDLT tape drive does not act as an initiator on the SCSI bus. Therefore, the drive does not:

1) generate unsolicited interrupts to the bus, 2) initiate its own SCSI commands, or 3) assert bus

reset.

• The SDLT 600 SCSI drive supports both LVD and single-ended bus configurations.

2.3 SCSI Bus Conditions

The SCSI bus has two asynchronous conditions:

• Attention Condition

• Reset Condition

2.3.1 Attention Condition

The Attention Condition informs an SDLT tape drive that an initiator has a message ready. The drive

gets the message by performing a MESSAGE OUT phase. The Attention Condition requires the

following timing:

• The initiator creates the Attention Condition by asserting ATN at any time except during the

ARBITRATION or BUS FREE phases.

• The initiator negates the ATN signal at least two deskew delays before asserting the ACK signal

while transferring the last byte of the message.

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Quantum 1200 Series DAT Autochanger Guía de usuario Pagina 26