IDE Register Addresses:
 

 The "x" being anywhere from 0 to 7, by jumper selection.
The IDE Driver (download page) uses the Inverted Register Set.

Registers	Normal/Read	Normal/Write	Inverted/Read	Inverted/Write
$FFx0	Data	Data	Status	Command
$FFx1	Error	Feature	Dev/Head	Dev/Head
$FFx2	Sec Count	Sec Count	Cyl High	Cyl High
$FFx3	Sec Number	Sec Number	Cyl Low	Cyl Low
$FFx4	Cyl Low	Cyl Low	Sec Number	Sec Number
$FFx5	Cyl High	Cyl High	Sec Count	Sec Count
$FFx6	Dev/Head	Dev/Head	Error	Feature
$FFx7	Status	Command	Data	Data
$FFx8	Latch	Latch	Latch	Latch
$FFx9	Alt Status	Alt Status	Alt Status	Alt Status
$FFxA	Drive Adrs	Drive Adrs	Drive Adrs	Drive Adrs