6.Command Specification | MODE SELECT |
Density Code: The supported values for the density code field are defined in the following table.
Table 6-40: Sequential-Access Density Codes
Code Value |
| Code Value |
30h | Format (not support) | |
31h | Format (not support) | |
32h | Format | |
B3h | Format | |
33h | Format | |
34h | Format | |
7Fh | No change from previous density |
Number of Blocks: A MODE SENSE field which will be returned as ZERO, indicating that all of the remaining logical blocks on the media will have the medium characteristics specified by the block descriptor, or until a subsequent MODE SELECT command changes those parameters. This field must be set to ZERO on a MODE SELECT otherwise a CHECK CONDITION status will be returned with an ILLEGAL REQUEST sense key.
Block length: The Block Length field specifies the length in bytes of each logical block. A block length of ZERO indicates that the length is variable. Any other value indicates the number of bytes per block that the drive must handshake over the bus. This establishes block length such that the transfer length for read, write type commands will be a block count not a byte count.
Note: It is value of this field together with the Fixed bit Field in the READ, or WRITE commands that determine whether the drive is in Fixed or Variable block mode.
Mode | Fixed Bit in Read, Write | Block Length in |
|
| Mode Select/Sense |
Fixed Block | 1 | Block Size |
Variable Block | 0 | 0 |
The default fixed block size is 0 bytes however, if a fixed command (fixed bit of ONE) is received, the drive will return the CHECK CONDITION status with an ILLEGAL REQUEST sense key and the ASC will be set to
COMMAND SEQUENCE ERROR.
Note: Minimum
Following the Block Descriptor are the MODE SELECT pages. They are the method by which the device parameters are set. Each page has a two byte header which identifies the page code and indicates the number of bytes in that page.
Table 6-41: MODE SELECT Page Header
Bit | 7 | 6 | 5 | 4 | 3 |
| 2 | 1 | 0 |
Byte |
|
|
|
|
|
|
|
|
|
0 | PS | Reserved |
|
| Page | Code |
|
|
|
1 |
|
|
| Additional Page Length |
|
|
|
PS: when the Page Savable bit is set, this indicates that the page contains saved parameters. This bit will never be set as there is no
SONY |