Samsung 3.5" hard disk drives, spinpoint v40 manual At Command Register Descriptions

DISK DRIVE OPERATION

6.4At Command Register Descriptions

Commands are issued to the drive by loading the pertinent registers in the command block with the needed parameters, and then writing the command code to the Command register. The manner in which a command is accepted varies. There are three classes of command acceptance (see Table 6-4), all based on the fact that to receive a command, BSY=0:

•Upon receipt of a Class 1 command, the drive sets BSY within 400 nsec.

•Upon receipt of a Class 2 command, the drive sets BSY within 400 nsec, sets up the sector buffer for a write operation, sets DRQ within 700 ∝ sec, and clears BSY within 400 nsec of setting DRQ.

•Upon receipt of a Class 3 command, the drive sets BSY within 400 nsec, sets up the sector buffer for a write operation, sets DRQ within 20 msec, and clears BSY within 400 nsec of setting DRQ.

NOTE: DRQ may be set so quickly on Class 2 and Class 3 that the BSY transition is too short for BSY=1 to be recognized.

If a new command is issued to a drive which has an uncompleted command (subsequently referred to as Old_Command) in progress, the drive immediately responds to the new command (subsequently referred to as New_Command), even if execution of the Old_Command could have been completed.

SpinPoint V40 Product Manual 53