Specifications

4.0 ATA interface I/O registers

The drive communicates with the host system through an I/O register

that routes the input and output data between registers. These registers

are selected by codes on the CS1FX–, CS3FX–, DA2, DA1, DA0, DIOR–

(read) and DIOW– (write) lines from the host.

The I/O register routes data between 14 registers. Ten registers are used

for commands to the drive or status reports from the drive, one register

is used for data, and three registers are used for control and alternate

status.

These registers can be divided into two groups: Command Block regis-

ters and Control Block registers, as shown in the following table. The

PC-AT I/O port addresses shown in the table below and in subsequent

text are for the primary host adapter address. Other PC-AT I/O port

addresses may be possible depending on the type of host adapter used.

Abbreviations: 1 = signal asserted; 0 = signal negated; X = doesn’t matter

Signal name

Function / Register

selected

PC-AT

I/O port

address

CS1FX– CS3FX– DA2 DA1 DA0 DIOR– DIOW–

0 0 X X X No operation —

1 1 X X X Invalid addressing —

0 1 X X X Selects Command Block —

1 0 X X X Select Control Block —

Command Block registers

1 0 0 0 0 Data register 1F0

1 0 0 0 1

Error

Feature

1F1

1 0 0 1 0 Sector Count register 1F2

1 0 0 1 1 Sector Number register 1F3

1 0 1 0 0 Cylinder Low register 1F4

1 0 1 0 1 Cylinder High register 1F5

1 0 1 1 0 Drive/Head register 1F6

1 0 1 1 1

Status

Command

1F7

ATA Interface Reference Manual, Rev. C 13