WRIEWrite and Invalidate Enable0

This bit, when set, causes the issuing of Write and Invalidate commands on the PCI bus whenever legal. The Write and Invalidate Enable bit in the PCI Configuration Command register must also be set in order for the chip to generate Write and Invalidate commands.

Registers: 0x1C–0x1F

Temporary (TEMP)

Read/Write

31

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TEMP

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

0

0

0

0

0

0

 

0

0

 

0

0

0

0

0

0

0

 

0

0

0

0

0

0

0

0

0

0

0

0

0

0

 

0

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TEMP

 

 

 

Temporary

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[31:0]

This 32-bit register stores the Return instruction address pointer from the Call instruction. The address pointer stored in this register is loaded into the DMA SCRIPTS Pointer (DSP) register when a Return instruction is executed. This address points to the next instruction to execute. Do not write to this register while the LSI53C875A is executing SCRIPTS.

During any Memory-to-Memory Move operation, the contents of this register are preserved. The power-up value of this register is indeterminate.

Register: 0x20

DMA FIFO (DFIFO)

Read/Write

7

0

BO

0

0

0

0

0

0

0

0

BOByte Offset Counter[7:0]

These bits, along with bits [1:0] in the Chip Test Five (CTEST5) register, indicate the amount of data transferred between the SCSI core and the DMA core. It is used to determine the number of bytes in the DMA FIFO when an interrupt occurs. These bits are unstable

SCSI Registers

4-57

Page 149
Image 149
LSI 53C875A technical manual Registers 0x1C-0x1F, Temp, DMA Fifo Dfifo