5.2 Logical Interface
(2)Features Field (exp)
The Features Field provides specific feature to a command. For instance, it is used with SET FEATURES command to enable or disable caching.
(3)Sector Count Field (exp)
The Sector Count Field indicates the number of sectors of data to be transferred in a read or write operation between the host system and the device. When the value in this field is X '00', the sector count is 256. With the EXT system command, the sector count is 65536 when value of the Sector Count Field is X '00' and that of the Sector Count Field (exp) is X '00'.
When this field indicates 0 at the completion of the command execution, this indicates that the command is completed successfully. If the command is not completed successfully, this field indicates the number of sectors to be transferred to complete the request from the host system. That is, this field indicates the number of remaining sectors that the data has not been transferred due to the error. However, as of the last sector of PIO transfer, SC=1 indicates the normal completion.
The contents of this field also have other definitions (Refer to 5.4)
(4)Sector Number Field (exp)
The contents of this field indicate the starting sector number for the subsequent command. The sector number should be between X '01' and [the number of sectors per track defined by INITIALIZE DEVICE PARAMETERS command.
Under the LBA mode, this field indicates LBA bits 7 to 0. Under the LBA mode of the EXT system command, LBA bits 31 to 24 are set in the Sector Number Field, and LBA bits 7 to 0 are set in the Sector Number Field (exp).
(5)Cylinder Low Field (exp)
The contents of this field indicate
At the end of a command, the contents of this field are updated to the current cylinder number.
Under the LBA mode, this field indicates LBA bits 15 to 8. Under the LBA mode of the EXT system command, LBA bits 39 to 32 are set in the Cylinder Low Field, and LBA bits 15 to 8 are set in the Cylinder Low Field (exp).