Data Or Scatter/Gather List Length; Status Block Pointer - Adaptec AHA-1740A Technical Reference Manual

EISA-to-Fast SCSI Host Adapter
1F 1E 1D 1C 1B 1A 19 18 17 16 15 14 13 12 11 10
The data lengths must be less than 4 MBytes and the total length of the transfer
must be less than 16 MBytes.

Data or Scatter/Gather List Length

This 32-bit field contains the length in bytes (least significant byte first) of the data
transfer. The host should always store a value in this field (even if data transfer is to
be suppressed), if a data phase is expected during the SCSI command. Otherwise, a
data overrun error will occur. If no data transfer is expected, this field should be set
to 0. The data lengths must be less than 4 MBytes.
If the Scatter/Gather flag (Flag Word 1, bit 12) is set to one, this field contains the
length in bytes of the Scatter/Gather list. This value must be nonzero and a multiple
of eight (8), otherwise, a specification error will be reported by the host adapter. The
length of the Scatter/Gather list is limited to 1 KByte.

Status Block Pointer

This 32-bit field contains the physical memory address (least significant byte first) of
the status block. The status block is written to by the host adapter and used by the
host to determine the completion status of a control block operation.
The length of the status block is always 32 bytes, though the number of bytes stored
by the host adapter may be less.
This field is required for all control blocks. However, the host adapter will bypass
writing to the status block if the control block completes without error and the Dis-
able Status Block flag (Flag Word 1, bit 14) is set to one.
Enhanced Mode Firmware Description
F E D C B A
Data Pointer 1
Data Length 1
Data Pointer 2
Data Length 2
.
.
.
Data Pointer n
Data Length n
9 8 7 6 5 4 3 2 1 0
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