U4 Family Product Manual, Rev. D 29
3.2.3 Set Features command
This command controls the implementation of various features that th e
drive supports. When the drive receives this command, it sets BSY,
checks the contents of the Features register, clears BSY and g enerates
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 accepta ble
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 IH
0=40-conductor cable detected, CBLID below VIL
02HEnable write cache

(default).

03HSet transfer mode (based on value in Sector Co unt register).
Sector Count register values:
00HSet PIO mode to default (PIO mode 2).
01HSet PIO mode to default and disable IORDY (PIO mode 2).
08HPIO mode 0
09HPIO mode 1
0AHPIO mode 2
0BHPIO mode 3
0CHPIO mode 4

(default)

20HMultiword DMA mode 0
21HMultiword DMA mode 1
22HMultiword DMA mode 2
40HUltra DMA mode 0
41HUltra DMA mode 1
42HUltra DMA mode 2
43HUltra DMA mode 3
44HUltra DMA mode 4