LSI 53C875A - Manual (Page 185)

SCSI Registers 4-93
STW SCSI FIFO Test Write 0
Setting this bit places the SCSI core into a test mode in
which the FIFO is easily read or written. While this bit is
set, writes to the least significant byte of the
SCSI Output
Data Latch (SODL) register cause the entire word
contained in the SODL to be loaded into the FIFO. These
functions are summarized in the table below.
Registers: 0x50–0x51
SCSI Input Data Latch (SIDL)
Read Only
SIDL SCSI Input Data Latch [15:0]
This register is used primarily for diagnostic testing,
programmed I/O operation, or error recovery. Data
received from the SCSI bus can be read from this
register. Data can be written to the
SCSI Output Data
Latch (SODL) register and then read back into the
LSI53C875A by reading this register to allow loopback
testing. When receiving SCSI data, the data flows into
this register and out to the host FIFO. This register differs
from the
SCSI Bus Data Lines (SBDL) register; SIDL
contains latched data and the SBDL always contains
exactly what is currently on the SCSI data bus. Reading
this register causes the SCSI parity bit to be checked,
and causes a parity error interrupt if the data is not valid.
The power-up values are indeterminate.
Register
Name
Register
Operation FIFO Bits
FIFO
Function
SODL Write [15:0] Load
SODL0 Write [7:0] Load
SODL1 Write [15:8] None
15 0
SIDL
x x x x x x x x x x x x x x x x