Specifications

example, if nHS3– through nHS0– are 1 1 0 0, respectively,

Head 3 is selected.

nDS1 is the drive select bit for drive 1 (the slave drive), and should be

active low when drive 1 is selected.

nDS0 is the drive select bit for drive 0 (the master drive), and should

be active low when drive 0 is selected.

4.8 Drive/Head register

The host selects between the master and slave drives based on the DRV

bit in the drive/head register. When the DRV bit is not set, the master

drive is selected, and when the DRV bit is set to 1, the slave drive is

selected. Seagate drives are designated as master and slave by setting

the appropriate jumpers.

CS1FX– = 1 DA2 = 1

CS3FX– = 0 DA1 = 1

DA0 = 0 Mode = Read/Write

PC-AT I/O port address: 1F6

The Drive/Head register contains the drive address and the head ad-

dress. At the end of a command, this register is updated to reflect the

currently selected head. This register is reset during a host reset or when

the Execute Drive Diagnostic command is issued. With logical block

addressing, this register contains bits 27 through 24 of the LBA.

The map of the Drive/Head register is shown below:

Bit 7 6 5 4 3 2 1 0

Name 1 LBA 1 DRV HEAD

DRV is the bit used to select the drive. Master is 0. Slave is 1.

HEAD is the 4-bit address used to select the head. When the drive is

executing the Initialize Drive Parameters command, HEAD

specifies the maximum head address.

LBA signifies the addressing scheme currently being used. If this bit

is set to 1, the drive is using the logical block addressing scheme.

If the bit is set to 0, the CHS scheme is used. Refer to Section

5.1 for an explanation of these two addressing schemes.

18 ATA Interface Reference Manual, Rev. C