5.7.2 Read/Write System Memory from SCRIPTS

By using the Memory Move instruction, single or multiple register values are transferred to or from system memory.

Because the LSI53C875A responds to addresses as defined in the Base Address Register Zero (I/O) or Base Address Register One (MEMORY) registers, it can be accessed during a Memory Move operation if the source or destination address decodes to within the chip’s register space. If this occurs, the register indicated by the lower seven bits of the address is taken as the data source or destination. In this way, register values are saved to system memory and later restored, and SCRIPTS can make decisions based on data values in system memory.

The SFBR is not writable using the CPU, and therefore not by a Memory Move. However, it can be loaded using SCRIPTS Read/Write operations. To load the SFBR with a byte stored in system memory, first move the byte to an intermediate LSI53C875A register (for example, a SCRATCH register), and then to the SFBR.

The same address alignment restrictions apply to register access operations as to normal memory-to-memorytransfers.

5.7.3

Second Dword

 

-

 

 

 

 

31

 

 

 

0

 

 

 

 

 

 

 

DMA SCRIPTS Pointer Save (DSPS) Register

 

 

 

 

x x x x x x x x

x x x x x x x x

x x x x x x x x

x x x x x x x x

 

 

 

 

 

 

 

DSPS Register

[31:0]

 

 

These bits contain the source address of the Memory

 

 

Move.

 

5-34

SCSI SCRIPTS Instruction Set

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LSI 53C875A technical manual Read/Write System Memory from Scripts, Dsps Register 310