3. Operational Overview
19
IDE REGISTERS
The IDE Interface is composed of 10 register locations. Eight of these are decoded at
1F0h-1F7h, with the remaining two at 3F6h and 3F7h. The "I/O Register Addresses and
Functions" table below defines all of the register addresses and functions for these I/O
locations.
I/O Register Addresses and Functions
I/O PORT
I/O READ
I/O WRITE
ADDRESS
FUNCTION
FUNCTION
1F0h
†
Data Register
Data Register
1F1h
Error Register
Write Precompensation Reg.
1F2h
Sector Count
Sector Count
1F3h
Sector Number
Sector Number
1F4h
Cylinder Low
Cylinder Low
1F5h
Cylinder High
Cylinder High
1F6h
SDH Register
SDH Register
1F7h
Status Register
Command Register
3F6h
Alt. Status Reg.
Digital Output Register
3F7
‡
Drive Address Reg.
Not Used
These registers are described in greater detail in Chapter 4, "
IDE Interface
."
†
16-bit transfer
‡
3F7h is shared with the floppy disk interface
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