Avago Technologies LSI53C896 - Manual (Page 167)

SCSI Registers 4-55
Version 3.3 Copyright © 1998–2003 by LSI Logic Corporation. All rights reserved.
Register: 0x17
Mailbox One (MBOX1)
Read/Write
MBOX1 Mailbox One [7:0]
These are general purpose bits that may be read or
written while SCRIPTS are running. They also may be
read or written by the SCRIPTS processor.
Note: The host and the SCRIPTS processor code could
potentially attempt to access the same mailbox byte at the
same time. Using one mailbox register as a read only and
the other as a write only prevents this type of conflict.
Register: 0x18
Chip Test Zero (CTEST0)
Read/Write
FMT Byte Empty in DMA FIFO [7:0]
These bits identify the bottom bytes in the DMA FIFO that
are empty. Each bit corresponds to a byte lane in the
DMA FIFO. For example, if byte lane three is empty,
FMT3 is set. Because the FMT flags indicate the status
of bytes at the bottom of the FIFO, if all FMT bits are set,
the DMA FIFO is empty.
7 0
MBOX1
0 0 0 0 0 0 0 0
7 0
FMT
1 1 1 1 1 1 1 1