Compaq EN Series Technical Reference Manual page 105

5.2.1.3 IDE ATA Control Registers
The IDE controller of the 82586 decodes the addressing of the standard AT attachment (ATA)
registers for the connected drive, which is where the ATA control registers actually reside. The
primary and secondary interface connectors are mapped as shown in Table 5-3.
Table 5–3. IDE ATA Control Registers
Primary Secondary
I/O Addr. I/O Addr.
1F0h 170h
1F1h 171h
1F1h 171h
1F2h 172h
1F3h 173h
1F4h 174h
1F5h 175h
1F6h 176h
1F7h 177h
1F7h 177h
3F6h 376h
3F6h 376h
3F7h 377h
3F7h 377h
The following paragraphs describe the IDE ATA control registers.
Data Register, I/O Port 1F0h/170h
This register is used for transferring all data to and from the hard drive controller. This register
is also used for transferring the sector table during format commands. All transfers are high-
speed 16-bit I/O operation except for Error Correction Code (ECC) bytes during Read/Write
Long commands.
Error Register, I/O Port 1F1h/171h (Read Only)
The Error register contains error status from the last command executed by the hard drive
controller. The contents of this register are valid when the following conditions exist:
♦ Error bit is set in the Status register
♦ Hard drive controller has completed execution of its internal diagnostics
Table 5-3.
IDE ATA Control Registers
Register
Data
Error
Features
Sector Count
Sector Number
Cylinder Low
Cylinder High
Drive/Head
Status
Command
Alternate Status
Drive Control
Drive Address
n/a for hard drive
Compaq Deskpro EN Series of Personal Computers
First Edition - June 1998
Technical Reference Guide
R/W
R/W
R
W
R/W
R/W
R/W
R/W
R/W
R
W
R
W
R
W
Net PC and Small Form Factor Models
5-3