through 07 - Block Length

The Block Length field defines the length in bytes of each logical block described by the Block Descriptor. A value of 0 for the Block Length field indicates variable-length logical blocks. A value greater than 0 indicates fixed-length logical blocks.

The power-on default value for the block length is 400h (1,024) bytes. The limit on the block length is the maximum block length specified by the Read Block Limits data (see Section 16.2). That is, if the ND bit is set to 0, the maximum block length is 03C000h or 240 KBytes; if the ND bit is set to 1, the maximum block length is 28000h or 160 KBytes.

Notes:

If you specify a value between 28001h and 03C000h for the Block Length, the EXB-8500 automatically sets the ND bit to 0. If, however, you specify a number greater than 03C000h for the Block Length, the EXB-8500 returns Check Condition status with the sense key set to Illegal Request (5h).

If the value specified for the Block Length field is not divisible by 4 (or 2 if the EEPROM image is set for two-byte boundary disconnect), then even-byte disconnect is disabled when the EXB-8500 updates the logical block length.

For information about changing the power-on default for the block length, refer to Section 3.4.

12.4 Vendor-Unique Parameters

(Non-Page Format)

Bit Byte

7 6 5 4 3 2 1 0

00 CT RSVD ND RSVD NBE EBD PE NAL

01 Reserved P5

02 Motion Threshold

03 Reconnect Threshold

04 Gap Threshold

Field Definitions

These vendor-unique parameters apply only to non-page format (that is, when the PF bit in the CDB is set to 0).

Byte 00, Bit 7 - CT (Cartridge Type)

This bit defines what type of data cartridge is expected to be loaded as follows:

0 – P6 Cartridge Type - Domestic

1 – PI Cartridge Type - International (P5, P6 LEOT equivalency)

Note: You can set the CT bit only when the tape is positioned at LBOT.

Refer to Appendix C for information about data cartridge capacities and for an explanation of how the EXB-8500 autosizes data cartridges. For

information about changing the power-on default for the cartridge type, refer to Section 3.4.

Byte 00, Bit 6 - RSVD This bit is reserved.

Byte 00, Bit 5 - ND (No Disconnect During Data Transfer)

This bit indicates whether the EXB-8500 can disconnect from the initiator during the data transfer phase.

0 – The EXB-8500 can disconnect from the initiator during the data transfer phase.

1 – The EXB-8500 will not disconnect during the data transfer phase.

The power-on default for the ND bit is 0.

Restrictions when the ND bit is 0

The maximum logical block size allowed, in fixed or variable mode, is 240 KBytes (3C000h).

Restrictions when the ND bit is 1

If the logical block size specified by the Block Length field in the Block Descriptor is greater than 160 KBytes (28000h), setting the ND bit to 1 causes the EXB-8500 to return Check Condition status with the sense key set to Illegal Request (5h).

The total number of bytes that can be transferred as a result of a single WRITE or READ command, in fixed or variable mode, is 160 KBytes (28000h). That is, the total transfer length specified by the CDB must be 160 KBytes or less.

During a write operation, the data transfer from the initiator does not start until the number of bytes of available space in the EXB-8500’s buffer is greater than or equal to the total transfer length specified by the CDB.

During a read operation, the data transfer to the initiator does not start until all of the data requested by the CDB, up to a total transfer length of 160 KBytes, is resident in the EXB-8500’s buffer.

If the Reconnect Threshold byte is set to a value less than A0h or greater than C0h, it will be changed to A0h. This is necessary for proper buffer management.

Byte 00, Bit 4 - RSVD This bit is reserved.

Byte 00, Bit 3 - NBE (No Busy Enable)

This bit is included for EXB-8200 compatibility only. This bit is set to 1 in the MODE SENSE data and is ignored by the MODE SELECT command.

Byte 00, Bit 2 - EBD (Even Byte Disconnect)

This bit is used to enable disconnects on even-byte boundaries. Two options are available from EXABYTE to control what happens when the EBD bit is set to 1. Depending on EXB-8500’s EEPROM image, setting the EBD bit to 1 allows disconnects to occur on two-byte boundaries or on four-byte

boundaries.

0 – Disconnect on any byte

1 – Disconnect on even-byte (two-byte or four-byte) boundaries Notes:

If the logical block length specified by the Block Length field in the Block Descriptor is not divisible by 4 (or 2 if the EEPROM image is set for two-byte boundary disconnect), setting the EBD bit to 1 causes the EXB-8500 to return Check Condition status with the sense key set to Illegal Request (5h).

For information about changing the power-on default for even-byte disconnect, refer to Section 3.4.

Byte 00, Bit 1 - PE (Parity Enable)

This bit is used to enable parity checking on the SCSI bus. When this bit is set to 1, every byte received by the EXB-8500 is checked for parity.

0 – Parity checking disabled 1 – Parity checking enabled.

The power-on default value for PE is 1.

Note: For information about changing the power-on default for parity checking, refer to Section 3.4.

Byte 00, Bit 0 - NAL (No Auto Load)

This bit is used to disable the automatic loading of the tape into the tape path when a data cartridge is inserted into the EXB-8500.

0 – Auto loading enabled 1 – Auto loading disabled.

The power-on default value for NAL is 0.

Byte 01, Bits 7 through 1 - Reserved These bits are reserved.

Byte 01, Bit 0 - P5

This bit is set to indicate that the data cartridge loaded in the EXB-8500 is expected to be a P5, European data cartridge. When set to 1, this bit overrides the CT bit.

Note: You can set the P5 bit only when the tape is positioned at LBOT.

Refer to Appendix C for information about data cartridge capacities and for an explanation of how the EXB-8500 autosizes data cartridges. For

information about changing the power-on default for the cartridge type, refer to Section 3.4.