Table 5.1

SCRIPTS Instructions

 

 

 

Instruction

 

Description

 

 

 

Block Move

 

Block Move instruction moves data between the SCSI

 

 

bus and memory.

 

 

I/O or Read/Write

I/O or Read/Write instructions cause the LSI53C875A to

 

 

trigger common SCSI hardware sequences, or to move

 

 

registers.

 

 

Transfer Control

Transfer Control instruction allows SCRIPTS instructions

 

 

to make decisions based on real time SCSI bus

 

 

conditions.

 

 

Memory Move

Memory Move instruction causes the LSI53C875A to

 

 

execute block moves between different parts of main

 

 

memory.

 

 

Load and Store

Load and Store instructions provide a more efficient way

 

 

to move data to/from memory from/to an internal register

 

 

in the chip without using the Memory Move instruction.

 

 

 

Each instruction consists of two or three 32-bit words. The first 32-bit word is always loaded into the DMA Command (DCMD) and DMA Byte Counter (DBC) registers, the second into the DMA SCRIPTS Pointer Save (DSPS) register. The third word, used only by Memory Move instructions, is loaded into the Temporary (TEMP) shadow register. In an indirect I/O or Move instruction, the first two 32-bit opcode fetches is followed by one or two more 32-bit fetch cycles.

5.2.1 Sample Operation

This sample operation describes execution of a SCRIPTS instruction for a Block Move instruction.

The host CPU, through programmed I/O, gives the DMA SCRIPTS Pointer (DSP) register (in the Operating register file) the starting address in main memory that points to a SCSI SCRIPTS program for execution.

Loading the DMA SCRIPTS Pointer (DSP) register causes the LSI53C875A to fetch its first instruction at the address just loaded. This is from main memory or the internal RAM, depending on the address.

High Level SCSI SCRIPTS Mode

5-3

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LSI 53C875A technical manual Sample Operation, Scripts Instructions, Instruction Description