Information Technology Reference
In-Depth Information
Sector number register (1F3h)
This is a read/write 8-bit register which defines the start sector to be read, written or verified.
After each transfer to/from the disk, the register contains the last processed sector.
Cylinder register (1F4h/1F5h)
These are read/write 8-bit registers which define the LSB (1F4h) and MSB (1F5h) of the
cylinder number. The two registers are capable of containing a 16-bit value. In standard IDE
the cylinder number is 10-bit and can only vary from 0 to 1023 (0 to 2
10
-1). For E-IDE the
value can be a 16-bit value and can thus vary from 0 to 65 535 (0 to 2
16
-1). This is one of the
main reasons that E-IDE can address much more data than IDE.
Drive/head register (1F6h)
This is a read/write 8-bit register which defines the currently used head. Its definitions are:
7
b
6
b
5
b
4
b
3
b
2
b
1
b
0
HD
0
1
L
1
DRV
HD
3
HD
2
HD
1
where:
•
L -
set to 1 if LBA (logical block addressing) mode else set to 0 if CHS (EIDE only).
•
DRV -
set to 1 for the slave, else it is master.
•
HD
3
-HD
0
-
identifies the head number, where 0000 identifies head 0, 0001 identifies head
1, and so on.
Status register (1F7h)
The 1F7h register has two modes. If it is written to then it is a command register (see next
section) else, if it is read from, then it is a status register. The status register is a read-only 8-
bit register which contains status information from the previously issued command. Its defi-
nitions are:
7
b
6
b
5
b
4
b
3
b
2
b
1
b
0
ERR
BUSY RDY WFT SKT DRQ COR IDX
where:
•
BUSY -
set to 1 if the drive is busy.
•
RDY -
set to 1 if the drive is ready.
•
WFT-
set to 1 if there is a write fault.
•
SKT-
set to 1 if head seek positioning is complete.
•
DRQ -
set to 1 if data can be transferred.
•
COR -
set to 1 if there is a correctable data error.
•
IDX -
set to 1 identifies that the disk index has just passed.
•
ERR -
set to 1 identifies that the error register contains error information.
Command register (1F7h)
If the 1F7h register is written-to then it is a command register. The command register is a 8-
bit register can contain commands, such as:
