Read
Full
The READ FULL command allows the Initiator
to
request all available information fields for
the specified logical or physical block. This information includes the header, data, and
ECC
field contents. The Target returns
to
the Initiator a complete image of one physical block.
Included with the contents of the physical 'block is a header
that
defines the amount and type
of
data
available.
Note
For this command
to
succeed, the header of the sector prior
to
the requested
sector
must be readable.
Read Full Command Descriptor Block
(COB)
Bit
Byte
7
I
6
I
5
I
4
I
3
I
2
I
1
I
0
00
Opcode
=
FOH
01
Logical Unit
Number
I
Reserved
I
PHYS
02-05
(MSB=02)
Address
(LSB=05)
06
Reserved
07-08
(MSB=07)
Allocation
Length
(LSB=08)
09
Control
Byte
Address. This
field
specifies which block
to
return.
PHYS (Physical Address). The interpretation of the address is determined by the
state
of the
PHYS bit. If PHYS
is
set
to
zero (0), the Address field
is
treated
as
a logical block address
per normal conventions and all normal position verifications are performed. The first physical
block in the specified
logical
block is returned.
To
access all physical blocks, the Initiator must
use the
MODE SELECT command
to
set the logical block size equal
to
the physical block
size (normally 512 bytes).
Otherwise, only the first physical block in each logical block is
accessible.
..'
If
PHYS
is
set
to
one (1), the Address field is treated as a physical block address with the
Address field defined as follows:
• Byte
2:
Physical Cylinder Address (MSB)
•
Byte
3:
Physical Cylinder Address (LSB)
•
Byte
4:
Head Address
• Byte
5:
Physical Sector Address
Allocation Length.
This field specifies the number of bytes the Initiator is prepared
to
accept.
If
the number
of
bytes available from the Target is greater than
that
specified in the CDB, the
data
will be
truncated
to
the Allocation Length value. The typical allocation length for a device formatted
with a 512 byte
data
field is 548.
B·18 Vendor Unique Command Descriptions
DRAFT
1/18/93 09:58
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