AT INTERFACE and ATA COMMANDS
WA31273A / WA32543A / WA33203A / WA32163A / WA31083A / WA32162A 6-9
6-3
Logical Interface
6-3-1 General
6-3-1-1 Bit Conventions
Bit names are shown in all upper case letters except where a lower case n precedes a bit
name. This indicates that when nBIT=0 (bit is zero) the action is true and when nBIT=1
(bit is one) the action is false. If there is no preceding n, then when BIT=1 it is true, and
when BIT=0 it is false.
A bit can be set to one or cleared to zero and polarity influences whether it is to be
interpreted as true or false:
True BIT=1 nBIT=0
False BIT=0 nBIT=1
6-3-1-2 Environment
Data is transferred in parallel (16bits) either to or from host memory to the device’s
buffer under the direction of commands previously transferred from the host. The
device performs all of the operations necessary to properly write data to, or read data
from, the media. Data read from the media is stored in the device’s buffer pending
transfer to the host memory and data is transferred from the host memory to the
device’s buffer to be written to the media.
The devices using this interface shall be programmed by the host computer to perform
commands and return status to the host at command completion. When two devices are
daisy chained on the interface, commands are written in parallel to both devices; this is
true for all except the Execute Diagnostics command, only the selected device executes
the command. On an Execute Diagnostics command addressed to Device 0, both devices
shall execute the command, and Device 1 shall post its status to Device 0 via PDIAG-.
Drives are selected by the DEV bit in the Drive/Head Register (see 6.3.4.9), and by a
jumper or switch on the device designating it as either a Device 0 or as Device 1. When
DEV=0, Device 0 is selected. When DEV=1, Device 1 is selected. When devices are daisy
chained, one shall be set as Device 0 and the other as Device 1. When a single device is
attached to the interface it shall be set as Device 0.
Throughout this document, device selection always refers to the state of the DEV bit, the
position of the Device 0/Device 1 jumper or switch, or use of the CSEL pin.
A device can operate in either of two addressing modes, CHS or LBA, on a command by
command basis. A device which can support LBA mode indicates this in the register,
Sector Number register, Cylinder Low mode in the Device/Head register, Sector
Number register, Cylinder Low register, Cylinder High register and HS3-HS0 of the
Device/Head register contains the zero based-LBA.
This term defines the addressing mode of the device as being by physical sector address.
