AT INTERFACE and ATA COMMANDS
6-
42 WA31273A / WA32543A / WA33203A / WA3216A / WA31083A / WA32162A
6-6
Protocol Overview
Commands can be grouped into different classes according to the protocols followed for
command execution. The command classes with their associated protocols are defined
below.
For all commands, the host first checks if BSY=1, and should proceed no further unless
and until BSY=0. For most commands, the host will also wait for DRDY=1 before
proceeding. Those commands shown with DRDY=X can be executed when DRDY=0.
6-6-1 PIO Data in Commands
This class includes:
•
Identify Drive (ECh)
•
Read Buffer (E4h)
•
Read Long (22h)
•
Read Sector(s) (20h)
•
Read Multiple (C4h)
Execution includes the transfer of one or more 512 byte (>512 bytes on Read Long)
sectors of data from the drive to the host.
a) The host writes any required parameters to the Features, Sector Count, Sector
Number, Cylinder and Drive/Head registers.
b) The host writes the command code to the Command Register.
c) The drive sets BSY and prepares for data transfer.
d) When a sector of data is available, the drive sets DRQ and cleans BSY prior to
asserting INTRQ.
e) After detecting INTRQ, the host reads the Status Register, then reads on sector of
data via the Data Register. In response to the Status Register being read, the drive
negates INTRQ.
f) The drive clears DRQ. If transfer of another sector is required, the drive also sets BSY
and the above sequence is repeated from d).
