SCSI Functional Description 2-29
Figure 2.4 LSI53C875A Host Interface SCSI Data Paths
The following steps determine if any bytes remain in the data path when
the chip halts an operation:
Asynchronous SCSI Send
Step 1. Ifthe DMA FIFO size is set to 112 bytes (bit 5 of the Ch ip Test
Five (CTEST5) register cleared), look at the DMA FIFO
(DFIFO) and DMA Byte Counter (DBC) registers and calculate
if there are bytes left in the DMA FIFO. Tomake this calculation,
subtract the seven least significant bits of the DBC register from
the 7-bit value of the DFIFO register. AND the result with 0x7F
for a byte count between zero and 112.
If the DMA FIFO size is set to 944 bytes (bit 5 of the Chip Test
Five (CTEST5) register is set), subtract the 10 least significant
PCIInterface** PCIInterface** PCIInterface** PCIInterface**
DMAFIFO*
(8Bytes x 118) DMAFIFO*
(8Bytes x 118) DMAFIFO*
(8Bytes x 118) DMAFIFO*
(8Bytes x 118)
SODLRegister* SIDL Register* SODLRegister* SCSIFIFO**
(1or 2 Bytes x 31)
SCSIInterface** SCSIInterface** SODRRegister* SCSIInterface**
SCSIInterface**
Asynchronous
SCSISend Asynchronous
SCSIReceive Synchronous
SCSISend Synchronous
SCSIReceive
SWIDERegister SWIDERegister
**= Parity protected
*= No parity protection