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2-16
SYM53C876/876E Data Manual
Functional Description
SCSI Functional Description
(using bit 5 of the CTEST5 register), subtract
the 10 least significant bits of the DBC regis-
ter from the 10-bit value of the DMA FIFO
Byte Offset Counter, which consists of bits 1-
0 in the CTEST5 register and bits 7-0 of the
DMA FIFO register. AND the result with
3FFh for a byte count between 0 and 536.
2. Read bit 7 in the SSTAT0 and SSTAT2
register to determine if any bytes are left in the
SIDL register. If bit 7 is set in the SSTAT0 or
SSTAT2, then the least significant byte or the
most significant byte is full, respectively.
3. If any wide transfers have been performed
using the Chained Move instruction, read the
Wide SCSI Receive bit (SCNTL2, bit 0) to
determine whether a byte is left in the SWIDE
register.
Synchronous SCSI Receive
1. If the DMA FIFO size is set to 88 bytes,
subtract the seven least significant bits of the
DBC register from the 7-bit value of the
DFIFO register. AND the result with 7Fh for
a byte count between 0 and 88.
If the DMA FIFO size is set to 536 bytes
(using bit 5 of the CTEST5 register), subtract
the 10 least significant bits of the DBC regis-
ter from the 10-bit value of the DMA FIFO
Byte Offset Counter, which consists of bits 1-
0 in the CTEST5 register and bits 7-0 of the
DMA FIFO register. AND the result with
3FFh for a byte count between 0 and 536.
2. Read the SSTAT1 register and examine bits
7-4, the binary representation of the number
of valid bytes in the SCSI FIFO, to determine
if any bytes are left in the SCSI FIFO.
3. If any wide transfers have been performed
using the Chained Move instruction, read the
Wide SCSI Receive bit (SCNTL2, bit 0) to
determine whether a byte is left in the SWIDE
register.
Figure 2-4: SYM53C876 Host Interface SCSI Data Paths
PCI Interface
DMA FIFO
(32-bits x 134)
SODL Register
SCSI Interface
Asynchronous
SCSI Send
PCI Interface
DMA FIFO
(32-bits x 134)
SIDL Register
SCSI Interface
Asynchronous
SCSI Receive
PCI Interface
DMA FIFO
(32-bits x 134)
SODL Register
SODR Register
Synchronous
SCSI Send
PCI Interface
DMA FIFO
(32-bits x 134)
SCSI FIFO
(8 or 16 bits x 16)
SCSI Interface
Synchronous
SCSI Receive
SCSI Interface
SWIDE Register
SWIDE Register