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SCSI Operating Registers
SYM53C825A/825AE Data Manual
5-17
Register 0B (8B)
SCSI Bus Control Lines (SBCL)
Read Only
Bit 7
RE Q (SRE Q/ Status)
Bit 6
ACK (SACK / Status)
Bit 5
BSY (SBSY / Status)
Bit 4
SE L (SSE L/ Status)
Bit 3
AT N (SAT N/ Status)
Bit 2
MSG (SMSG/ Status)
Bit 1
C/D (SC_D/ Status)
Bit 0
I/O (SI_O/ Status)
When read, this register returns the SCSI con-
trol line status. A bit will be set when the corre-
sponding SCSI control line is asserted. T hese
bits are not latched; they are a true representa-
tion of what is on the SCSI bus at the time the
register is read. T he resulting read data is syn-
chronized before being presented to the PCI
bus to prevent parity errors from being passed
to the system. T his register can be used for
diagnostics testing or operation in low level
mode.
Register 0C (8C)
DMA Status (DSTAT )
Read Only
Reading this register will clear any bits that are set
at the time the register is read, but will not neces-
sarily clear the register because additional inter-
rupts may be pending (the SYM53C825A stacks
interrupts). T he DIP bit in the IST AT register will
also be cleared. DMA interrupt conditions may be
individually masked through the DIEN register.
When performing consecutive 8-bit reads of the
DST AT , SIST 0 and SIST 1 registers (in any or-
der), insert a delay equivalent to 12 CLK periods
between the reads to ensure that the interrupts clear
properly. See Chapter 2, “Functional Description,”
for more information on interrupts.
Bit 7
DFE (DMA FIFO E mpty)
T his status bit is set when the DMA FIFO is
empty. It may be used to determine if any data
resides in the FIFO when an error occurs and
an interrupt is generated. T his bit is a pure sta-
tus bit and will not cause an interrupt.
Bit 6
MDPE (Master Data Parity E rror)
T his bit is set when the SYM53C825A as a
master detects a data parity error, or a target
device signals a parity error during a data
phase. T his bit is completely disabled by the
Master Parity Error Enable bit (bit 3 of
CT EST 4).
Bit 5
BF (Bus Fault)
T his bit is set when a PCI bus fault condition
is detected. A PCI bus fault can only occur
when the SYM53C825A is bus master, and is
defined as a cycle that ends with a Bad Address
or Target Abort Condition.
REQ
7
Default>>>
X
ACK
6
BSY
5
SEL
4
ATN
3
MSG
2
C/D
1
I/O
0
X
X
X
X
X
X
X
DFE
7
MDPE
6
BF
5
ABRT
4
SSI
3
SIR
2
RES
1
IID
0
Default>>>
1
0
0
0
0
0
X
0