Dma Data Transfer Commands - IBM IC25N020ATDA04 - Travelstar 20 GB Hard Drive Specifications

12.4 DMA Data Transfer commands

These commands are
! Identify Device DMA
! Read DMA
! Write DMA
Data transfers using DMA commands differ in two ways from PIO transfers:
! Data transfers are performed using the Slave DMA channel
! No intermediate sector interrupts are issued on multisector commands
Initiation of the DMA transfer commands is identical to the Read Sector or Write Sector commands. The
difference is that the host does not initializes the Slave DMA channel prior to issuing the command.
The interrupt handler for DMA transfers differs as follows:
! No intermediate sector interrupts are issued on multisector commands.
! The host resets the DMA channel prior to reading status from the device.
The DMA protocol allows high performance multitasking operating systems to eliminate processor
overhead associated with PIO transfers.
1. The host initializes the Slave DMA channel.
2. The host writes any required parameters to the Features, Sector Count, Sector Number, Cylinder and
Device/Head registers.
3. The host writes command code to the Command Register.
4. The device sets DMARQ when it is ready to transfer any part of the data.
5. The host transfers the data using the DMA transfer protocol currently in effect.
6. When all of the data has been transferred, the device generates an interrupt to the host.
7. The host resets the Slave DMA channel.
8. The host reads the Status Register and, optionally, the Error Register.
Travelstar 48GH, 30GN & 15GN hard disk drive specifications
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