Command Control Byte; Table 4-3: The Command Control Byte - Tandberg Data SLR7-140 PROGRAMMER Manual

LUN
Parameters
Control Byte
BYTE BIT 7
Last Byte X
X
RESERVED
NACA
Link
Flag
Tandberg Data
The Drive supports only one Logical Unit Number (LUN).
This field should/must be set to zero in all Command
Descriptor Blocks for the Drive.
The Drive is a SCSI-1/2 compliant device. The Drive will
ignore the LUN specified in the CDB if an IDENTIFY
message was received. It is recommended that the LUN in
the CDB be set to zero. See section 4.6.3. Commands
Received Serially, LUN Not 0 for a description of the
response to non-zero LUN values.
See the specific commands for detailed information on
the various parameter bytes.
See Section 4.2. for details on the Command Control
Byte.
4.2.

Command Control Byte

The Control Byte
Descriptor Block. A typical Control Byte is shown below.
6 5
X RESERVED

Table 4-3: The Command Control Byte

Bits 6 and 7
exception is the SPACE command which uses control byte
bit 7 as its FAST option bit.
These bits MUST always be set to zero.
The Normal ACA (NACA) bit must be set to zero.
If the Link bit is set, an automatic link to the next
command is made
current command. The Drive first returns INTERMEDIATE
status for the current command (instead of GOOD status),
it then returns
messages (as described under Flag below) before going
directly to another Command Phase (there is no Bus Free
phase in between commands).
When the Link bit and the IMMediate bit of a command
(where applicable)
returns CHECK CONDITION status. The Error Code is set to
I F I CDB.
NVALID IELD N
The Flag bit is only meaningful when the Link bit is set
to one. If both bits are set, a LINKED COMMAND COMPLETE
WITH FLAG message byte is sent after the INTERMEDIATE
status byte. If only the Link bit is set, a LINKED
COMMAND COMPLETE
INTERMEDIATE status byte.
If only the Flag bit is set (the Link bit is zero), the
Drive returns CHECK CONDITION status. The Error Code is
set to I F
NVALID IELD
4-2 Tandberg SLR Product Line SCSI Functional Specifications
is the last
4 3
are ignored by
at a successful
one of two linked
are both set
message byte
I CDB.
N
Commands
byte of every
2 1
NACA Flag
the Drive. The
completion of
command complete
to one, the
is sent after
Command
0
Link
only
the
Drive
the