Specifications

5.2.1 PIO read commands

The PIO read command group includes the Identify Drive, Read Buffer,

Read Long, Read Multiple and Read Sectors commands. The Identify

Drive and Read Buffer commands each transfer a single block of 512

bytes. The Read Long command transfers a single block of 512 bytes

plus 4 or more ECC bytes. The Read Multiple command transfers one

or more blocks of data where the size of each block is a multiple of 512

bytes. The Read Sectors command transfers one or more blocks of 512

bytes each.

To execute a PIO read command, the host and drive follow these steps:

1. The host writes any required parameters to the Features, Sector

Count, Sector Number, Cylinder and Drive/Head registers.

2. The host writes the command code to the Command register.

3. The drive sets BSY and prepares for data transfer.

4. When a block of data is available, the drive sets DRQ and clears BSY

prior to asserting INTRQ.

5. After detecting INTRQ, the host reads the Status register. In response

to the Status register being read, the drive negates INTRQ.

6. The host reads one block of data from the Data register.

7. The drive clears DRQ. If transfer of another block is required, the drive

also sets BSY and the above sequence is repeated from step 4).

The following table shows a PIO read command that transfers two blocks

without an error (in this and subsequent tables, read downward to follow

the sequence of steps executed).

Step Event Process BSY DRQ INTRQ

1 — Setup BSY=0 — —

2 — Issue command BSY=0 — —

3 — — BSY=1 — —

Transfer

first

block

— BSY=0 DRQ=1 Assert

5 Read status BSY=0 DRQ=1 Negate

6 Transfer data BSY=0 DRQ=1 —

7 — BSY=1 — —

continued

ATA Interface Reference Manual, Rev. C 27