User's Guide

Page 110 DDS-4 SCSI Interface Manual, Rev. B
READ BLOCK LIMITS (05h)
The READ BLOCK LIMITS command causes the drive to transfer the block length
limits to the Initiator. The minimum block length is 1 byte; the maximum is 2
24
-1
bytes. The minimum and maximum block limits are returned to the Initiator in a six-
byte data string.
READ BLOCK LIMITS 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 0 1 0 1
1 0 0 0 0 0 0 0 0
2 0 0 0 0 0 0 0 0
3 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 0 0
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 Command Descriptor Block does not contain command dependent fields. The
values of the individual bytes in the Block Length fields are shown in the following
table in hexadecimal notation.
Byte
Bits
7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 0 0
1 MSB—Maximum Block Length (FFH)
2 Maximum Block Length (FFh)
3 Maximum Block Length—LSB (FFh)
4 MSB—Minimum Block Length (00h)
5 Minimum Block Length—LSB (01h)
Block Size Definition
The host specifies the actual block size in fixed mode with the MODE SELECT
command and in variable with the transfer/allocation length of READ and WRITE
commands. The use of the MODE SENSE command determines the current block
size. The READ BLOCK LIMITS command indicates the minimum and maximum
block size that the drive can support. Because the MODE SELECT block descriptor
block size field is 3 bytes in length, the drive is logically limited to this imposed limit.
Therefore, the maximum block size is ffffff hexadecimal or 16,777,215 bytes in
length.