AT INTERFACE and ATA COMMANDS
6-
14 WA31273A / WA32543A / WA33203A / WA3216A / WA31083A / WA32162A
6-3-4-5 Sector Count Register (1F2h)
This register contains the number of sectors of data requested to be transferred on a read
or write operation between the host and the drive. If the value in this register is zero, a
count of 256 sectors is specified.
If this register is zero at command completion, the command was successful. If not
successfully completed, the register contains the number of sectors which need to be
transferred in order to complete the request.
The contents of this register may be defined otherwise on some commands (e.g.
Initialize Drive Parameters, Format Track commands).
6-3-4-6 Cylinder High Register (1F5h)
In
CHS
mode this register contains the high order bits of the starting cylinder address
for any disk access. In
LBA
mode this register contains bits 8-15 of the LBA.
At the end of the command, this register is updated to reflect the current disk address.
The most significant bits of the cylinder address are loaded into the Cylinder High
Register.
6-3-4-7 Cylinder Low Register (1F4h)
In
CHS
mode this register contains the low order 8 bits of the starting cylinder address
for any disk access. In
LBA
mode this register contains bits 16-23 of the LBA. At the end
of the command, this register is updated to reflect the current disk address.
6-3-4-8 Command Register (1F7h)
This register contains the command code being sent to the drive. Command execution
begins immediately after this register is written. The executable commands, the
command codes, and the necessary parameters for each command are listed in Table 6-4.
6-3-4-9 Drive/Head Register (1F6h)
This register contains the drive and head numbers. When executing an Initialize Drive
Parameters command, the contents of this register defines the number of heads minus 1.
7
6
5
4
3
2
1
0
1
LBA
1
DEV
HS3
HS2
HS1
HS0
•
DRV
is the binary encoded drive select number. When DEV=0, Device 0 is selected.
When DEV=1, Device 1 is selected.
