SCS I Description
M axtor Atlas 10K III 5-119
The READ S KI P MASK command allows the init i a tor to c ondit i on the f unct ion of
the READ commands to allow only selected data to be transferred over the SCSI
interface. A READ SKIP MASK comm an d precedes a REA D (10) command; the
READ (10) command must be linked to the READ SKIP MASK command or the
skip mask is lost and a CHECK CONDITION status is returned. The data format and
field descriptions are shown in Table 5-149 and Table 5-150 r especti vely .
READ SKIP MAS K Comman d - Data Format
READ SKIP MASK Command-Field Descriptions
0 Opera tion C ode (E 8h )
1 Reserved
2 - 5 (MSB) Logical Block Address (LSB)
6 Skip Mask Length
7 - 8 (MSB) Transfer Length (LSB)
9 VU Reserved Flag Link
Logical Block Address
This field specifies the first logical block of the corresponding READ (10)
COMMAND. This allows a SEEK to begin immediately. The LBA of the fol-
lowing READ (1 0) comm and mus t the same as the LBA of the READ SKIP
MASK com mand.
Skip Mask Length
This field indicates the length i n bytes of t h e skip m ask. Th e m ask is up to
2048 bits, giving a data address capabil ity of 1 MB in 512-byte bl ock
length. The mask consists of a sequence of bit s whe re a “1” bit is for the
block s of dat a t o be tra nsferr ed, and a “0” f or the bl ocks of data tha t ar e to
be skipped. The first “1” bit of the mask co rresponds to the first LBA to be
transferred . Any unused bits at the end of the las t byt e in the m ask m ust
be set to 0. The mask is transferred in t he data-out buff er transfer of the
skip m ask com mand.
Transfer Length
This field mu st be equal to the transf er leng th in the linked READ (10) com-
mand. The t rans fer leng th field m ust be equal to the number of “1” bits in
the skip mask. If a READ (10) is used with 0 as the transfer length, a trans-
fer length of 256 data blocks is implied.