Specifications

ATAPI For Streaming Tape QIC-157 Rev B
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Table 6-2 Typical Command Packet for Read or Write Operations
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code
1 Reserved 1 (BT)
2 (MSB)
3 Transfer Length
4 (LSB)
5 Reserved
6 Reserved
7 Reserved
8 Reserved
9 Reserved
10 Reserved
11 Reserved
6.2.1. Operation Code
The operation code of the Command Packet has a group code field and a command code field. The
three-bit group code field provides for eight groups of command codes. The five-bit command code
field provides for thirty-two command codes in each group. Thus, a total of 256 possible operation
codes exists. Operation codes are defined in the subsequent sections.
Table 6-3 Operation Code
Bit 7 6 5 4 3 2 1 0
Group Code Command Code
Note that the Group/Command code fields have been kept for backward compatibility and are not
used by ATAPI.
6.2.2. Logical Block Address
The logical block address shall begin with block zero and be contiguous up to the last logical block.
6.2.3. Transfer Length
The Transfer Length Field specifies the amount of data to be transferred, usually the number of
blocks. For several commands the transfer length indicates the requested number of bytes to be sent
as defined in the command description. For these commands the Transfer Length Field may be
identified by a different name. See the following descriptions and the individual command
descriptions for further information.
In commands that use multiple bytes for the transfer length, a transfer length of zero indicates that
no data transfer shall take place. A value of one or greater indicates the number of blocks that shall
be transferred.
6.2.4. Parameter List Length
The Parameter List Length is used to specify the number of bytes to be sent to the Device. This field
is typically used in Command Packets for parameters that are sent to a Device (e.g. mode