Specifications

4.2 Command register
CS1FX– = 1 DA2 = 1
CS3FX– = 0 DA1 = 1
DA0 = 1 Mode = Write Only
PC-AT I/O port address: 1F7
H
This eight-bit register contains the host command. When this register is
written, the drive immediately begins executing the command. The host
must ensure that the BSY bit in the Status register is set to 0. All other
setup registers must be written to (with appropriate values) before the
command register can be written. Refer to Section 5.3.1 for an explana-
tion of the command register’s contents following the execution of various
commands.
4.3 Cylinder High register
CS1FX– = 1 DA2 = 1
CS3FX– = 0 DA1 = 0
DA0 = 1 Mode = Read/Write
PC-AT I/O port address: 1F5
H
This register contains the most significant bits of the starting cylinder
address for any disc access. At the completion of a command, this
register is updated to reflect the current cylinder address.
With logical block addressing, this register contains bits 23 through 16
of the LBA.
ATA Interface Reference Manual, Rev. C 15