Quantum 1200 Series DAT Autochanger Uživatelská příručka stáhnout pdf (Strana 42)

Supported SCSI Messages SDLT 600 SCSI Interface Guide

3-14 January 2005 81-81200-02 REV A01

3.2.16 WIDE DATA TRANSFER REQUEST (extended message

03h)

Figure 3-6 illustrates the message formats.

Figure 3-6. WIDE DATA TRANSFER REQUEST Message — Data Format

The SDLT tape drive initiates a WIDE DATA TRANSFER REQUEST message exchange whenever a

previously arranged transfer width agreement may have become invalid. The agreement becomes

invalid after any condition that may leave the data transfer agreement in an indeterminate state, such

as:

• After a hard reset condition

• After a TARGET RESET message

• After a power cycle.

The WIDE DATA TRANSFER REQUEST message exchange establishes an agreement between two

SCSI devices on the width of the data path to be used for DATA phase transfer between them. This

agreement applies to DATA IN and DATA OUT phases only. All other information transfer phases

must use an eight-bit data path.

The drive implements both the wide data transfer option and synchronous data transfer option. If both

wide and synchronous data transfers are used, the wide data transfer agreement must be negotiated

first. If a synchronous data transfer agreement is in effect, the drive resets the synchronous agreement

to asynchronous mode after accepting a WIDE DATA TRANSFER REQUEST message.

The transfer width established applies to all logical units. 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.

Bit

Byte

7 6 5 4 3 2 1 0

Extended Message Identifier (01h)

(see

Figure 3-1)

1 Extended Message Length (02h)

2 WIDE DATA TRANSFER REQUEST (03h)

3 Transfer Width Exponent

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 293 294

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Quantum 1200 Series DAT Autochanger Uživatelská příručka Strana 42