Seagate U4 ST36421A User Manual download pdf (Page 37)

U4 Family Product Manual, Rev. D 29

3.2.3 Set Features command

This command controls the implementation of various features that the

drive supports. When the drive receives this command, it sets BSY,

checks the contents of the Features register, clears BSY and generates

an interrupt. If the value in the register does not represent a feature that

the drive supports, the command is aborted. Power-on default has the

read look-ahead and write caching features enabled. The acceptable

values for the Features register are defined as follows:

11 Ultra DMA mode 3 is currently active.

12 Ultra DMA mode 4 is currently active.

Bit Word 93

13 1=80-conductor cable detected, CBLID above V

0=40-conductor cable detected, CBLID below V

Enable write cache

(default).

Set transfer mode (based on value in Sector Count register).

Sector Count register values:

Set PIO mode to default (PIO mode 2).

Set PIO mode to default and disable IORDY (PIO mode 2).

PIO mode 0

PIO mode 1

PIO mode 2

PIO mode 3

PIO mode 4

(default)

Multiword DMA mode 0

Multiword DMA mode 1

Multiword DMA mode 2

Ultra DMA mode 0

Ultra DMA mode 1

Ultra DMA mode 2

Ultra DMA mode 3

Ultra DMA mode 4

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Seagate U4 ST36421A User Manual Page 37