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SDLT 600 SCSI Interface Guide Chapter 3: SCSI Messages

81-81200-02 REV A01 January 2005 3-11

3.2.13 RESTORE POINTERS (03h)

The SDLT tape drive sends the RESTORE POINTERS message to the initiator to direct the initiator to

copy the most recently saved command, data, and status pointers for the I/O process to the

corresponding current pointers. The command and status pointers are restored to the beginning of the

present command and status areas. The data pointer is restored to the value at the beginning of the data

area in the absence of a SAVE DATA POINTER message or to the value at the point at which the last

SAVE DATA POINTER message occurred for that logical unit.

When the drive receives the RESTORE POINTERS message, it switches to the message in phase and

returns MESSAGE REJECT.

3.2.14 SAVE DATA POINTER (02h)

The SDLT tape drive sends the SAVE DATA POINTER message to direct the initiator to copy the

current data pointer to the saved data pointer for the current I/O process.

The drive sends this message before a disconnect during a data transfer. It may not send a SAVE DATA

POINTER message if it intends to move directly to the STATUS phase. If the drive receives this

message, it enters the message-in phase and returns MESSAGE REJECT.

Table 3-8. Features of the PARALLEL PROTOCOL REQUEST Message

Field Description

DT_REQ Double Transition Clocking Request. This bit indicates a request for Double

Transition Clocking, which means that two units of data are transferred for

each clock cycle. Support for the PPR message is indicated by the Clocking

field in the Standard Inquiry page.

Transfer Width

Exponent

Valid transfer widths for the SDLT tape drive are 8 bits (transfer width =

00h) and 16 bits (transfer width = 01h). Other transfer widths are reserved.

Transfer Period

Factor

09h = 12.5 nsec Transfer Period, 80 MHz

0Ah = 25 nsec Transfer Period, 40 MHz

0Ch = 50 nsec Transfer Period, 20 MHz

19h = 100 nsec Transfer Period, 10 MHz

32h = 200 nsec Transfer Period, 5 MHz

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Quantum 1200 Series DAT Autochanger Betriebsanweisung Seite 39