User's Guide

Commands: Read (08h) Page 105
READ (08h)
The READ command transfers one or more bytes or blocks from the drive to the
Initiator beginning with the next logical block on tape.
READ Command Descriptor Block
The following table shows the layout of the CDB.
Byte
Bits
7 6 5 4 3 2 1 0
0 0 0 0 0 1 0 0 0
1 0 0 0 0 0 0 SILI Fixed
2 MSB—Transfer Length
3 Transfer Length
4 Transfer Length—LSB
5 vendor unique* 0 0 0 0 Flag Link
* This vendor-unique field is reserved and must be set to zero.
Command Descriptor Block Field Description
The following table defines the fields in the CDB.
Field
Name Bytes Bits Description
Fixed bit 1 0 If this bit is 1, the size of the blocks is fixed, as specified by the
MODE SELECT Block Descriptor. If it is 0, the transfer length
contains the number of bytes in the block.
Suppress
Incorrect
Length
Indicator
1 1 The SILI (Suppress Incorrect Length Indicator) bit is used to
suppress incorrect length error reporting when reading variable-
length blocks.
If the SILI bit is 1 and the Fixed bit is 1, the drive returns a Check
Condition with Illegal Request sense key with an additional sense
code of Invalid Field in CDB.
When the SILI bit is 1 and Fixed bit is 0 and the only error
encountered by the drive is that the actual block length differs from
the requested transfer length, then the drive
• Returns a Check Condition if the actual block length is larger than
the requested transfer length and the Block Length field in the
Mode Parameter block descriptor is nonzero.
• Does not return a Check Condition if the actual block length is
smaller than the requested transfer length or if the actual block is
larger than the requested block and the block length in the Mode
Parameter block descriptor is 0.
Transfer 2-4 This field specifies the number of bytes or blocks to be read. When a
transfer length is 0, no data is transferred. This condition is not
considered an error.