AT INTERFACE and ATA COMMANDS
WA31273A / WA32543A / WA33203A / WA32163A / WA31083A / WA32162A 6-17
6-4
At 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 (see Table 6-4) of command acceptance, 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
µ
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.
Table 6-4.
Command Codes and Parameters
COMMAND
PARAMETER USED
Class
DESCRIPTION
CODE
FR
SC
SN
CY
DH
1
Execute Device Diagnostic
90h
D*
2
Format Track
50h
d
1
Identify Device
ECh
D
1
Idle
97h,E3h
y
D
1
Idle Immediate
95h,E1h
D
1
Initialize Drive Parameter
91h
y
y
1
Read Buffer
E4h
1
Read DMA (w/retry)
C8h
y
y
y
y
1
Read DMA (w/o retry)
C9h
y
y
y
y
