Table
5.5.
Host Command Block
Command Class
Operation Code
BYTE WORD^
l
1
eg1
S
1
:l:
2 1(lg]
0
l
0
0
Command Class
OP
Code
1
0
Lo ical Unit Number Lo ical Sector Address Hi
h)
2
1 Lo ical Sector Address Middle)
3
1
4 2
5
2
Logical Sector Address (Low)
Block (sector) Count
Control
Bvte (reserved in DMA s~ec)
10
5
11
5
12
6
Byte
0
must be specified for all commands. Depending on the value of
Byte
0,
each parameter in Bytes
1
through
5
may require specification.
Table
6.2
specifies the supported commands and their parameters.
It
also includes information in data transfers required during execution.
All other commands are reserved.
Reserved
Reserved
ADV
I
Error Tvoe
I
Error Code
13
6
14
7
15
7
There are eight command classes. Command class
0
contains the
commands used in normal operation. Command class
7
contains the
diagnostic commands. Command classes
l,
2,4,
5,
and
6
are re-
served for future use.
There are
32
operation codes in each command class. For a descrip-
tion of all the available op codes see the Command Description Sec-
tion.
LUN
Logical
Unit
Number
This
is
contained in the upper three bits of Byte
1
specifyfing one of
eight logical unit numbers. Logical units
0
and
1
are hard disk drives
0
and
1
respectively. Logical units
2
and
7
are reserved for future
use. The HDC reports an invalid command if the logical unit number
is out of range. However, for error reporting, all even LUN's are
treated as drive
0
and all odd
LUN's
are treated as drive
1.
LADD
2
LADDl
LADDO
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