Specifications

4.10 Features register

CS1FX– = 1 DA2 = 0

CS3FX– = 0 DA1 = 0

DA0 = 1 Mode = Write Only

PC-AT I/O port address: 1F1

This register is used by the Set Features command to enable and disable

special options, as defined in Section 5.4.14 (The Set Features command).

4.11 Sector Count register

CS1FX– = 1 DA2 = 0

CS3FX– = 0 DA1 = 1

DA0 = 0 Mode = Read/Write

PC-AT I/O port address: 1F2

This register specifies the number of sectors of data to be transferred

during read/write sector commands. The value contained in the register

is decremented every time a sector is transferred. A value of zero

specifies 256 sectors. When executing the Initialize Drive Parameters or

Format commands, this register defines the number of sectors per track.

This register is used by the power mode commands to set timers.

4.12 Sector Number register

CS1FX– = 1 DA2 = 0

CS3FX– = 0 DA1 = 1

DA0 = 1 Mode = Read/Write

PC-AT I/O port address: 1F3

This register contains the starting sector number for any disc access. At

the completion of a command, this register is updated to reflect the last

sector transferred correctly, or the sector on which an error occurred. The

sectors are numbered sequentially, starting with 1. With logical block

addressing, this register contains bits 7 through 0 of the logical block

address (LBA).

20 ATA Interface Reference Manual, Rev. C