Commodore Amiga A500 Technical Reference Manual page 176

Command Class
Operation Code
Logical Unit Number
Table 5.5. Host Command Block
BYTE WORD 7
0 0 Command Class
1 0 Logical Unit Number Logical Sector Address (High)
2 1
3 1
4 2
5 2
6 3
7 3
8 4
9 4 Reserved
10 5 Reserved
11 5 Reserved
12 6 ADV
13 6
14 7
15 7 LADD0
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.
There are eight command classes. Command class 0 contains the
commands used in normal operation. Command class 7 contains the
diagnostic commands. Command classes 1, 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.
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.
173
6 5 4
OP Code
Logical Sector Address (Middle)
Logical Sector Address (Low)
Block (sector) Count
Control Byte (reserved in DMA spec)
High Order DMA DB Address (A23-A17)
Mid Order DMA DB Address (A15-A9)
Low Order DMA DB Address (A1-A8)
Error Type
LUN
LADD1
3 2 1 0
Error Code
LADD2