IBM DBCA-203240, Specifications

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11.4 DMA Data Transfer Commands
These commands are:
Identify Device D M A
Read D M A
Write D M A
Data transfer using D M A commands differ in two ways from PIO transfers:
data transfers are performed using the slave-DMA channel
no intermediate sector interrupts are issued on multi-sector commands
Initiation of the D M A transfer commands is identical to the Read Sector or Write Sector commands except
that the host initializes the slave-DMA channel prior to issuing the command.
The interrupt handler for D M A transfers is different in that:
no intermediate sector interrupts are issued on multi-sector commands
the host resets the D M A channel prior to reading status from the device.
The D M A protocol allows high performance multi-tasking operating systems to eliminate processor over-
head associated with PIO transfers.
1. Host initializes the slave-DMA channel
2. Host writes any required parameters to the Features, Sector Count, Sector Number, Cylinder and
Device/Head registers.
3. Host writes command code to the Command Register
4. The device sets D M A R Q when it is ready to transfer any part of the data.
5. Host transfers the data using the D M A transfer protocol currently in effect.
6. When all of the data has been transferred, the device generates an interrupt to the host.
7. Host resets the slave-DMA channel
8. Host reads the Status Register and, optionally, the Error Register
Command Protocol
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