Specifications

In contrast, the table below illustrates a PIO write command with an error

indicated on the first block.

Step Event Process BSY DRQ INTRQ

1 — Setup BSY=0 — —

2 — Issue command BSY=0 — —

3 — — BSY=1 — —

Transfer

first

block

Transfer data BSY=0 DRQ=1 —

5 — BSY=1 — —

6 — BSY=0 DRQ=1 Assert

7 Read status BSY=0 DRQ=1 Negate

5.2.3 DMA data transfer commands

The DMA data transfer commands are Read DMA and Write DMA. Data

transfers using DMA commands differ from PIO transfers in two ways:

1) data transfers are performed using the slave-DMA channel; and 2) a

single interrupt is generated by the drive at the completion of the

command.

Initiation of the DMA transfer commands is identical to the Read Sectors

or Write Sectors commands except that the host initializes the slave-DMA

channel prior to issuing the command.

The host interrupt handler for DMA transfers is different from PIO

transfers in that: 1) no intermediate sector interrupts are issued on

multisector commands; and 2) the host resets the DMA channel prior to

reading status from the drive.

The host and drive follow these steps to execute the DMA Read or DMA

Write commands:

1. The host initializes the slave-DMA channel.

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

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

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

4. The drive sets BSY.

5. The host and the drive transfer the data through the slave-DMA chan-

nel. A DMA transfer command with an error may transfer none, some,

30 ATA Interface Reference Manual, Rev. C