Sample Operation; Scripts Instructions - LSI LSI53C875A Technical Manual

5.2.1 Sample Operation

Table 5.1

SCRIPTS Instructions

Instruction
Block Move
I/O or Read/Write
Transfer Control
Memory Move
Load and Store
Each instruction consists of two or three 32-bit words. The first 32-bit
word is always loaded into the
Counter (DBC) registers, the second into the
Save (DSPS) register. The third word, used only by Memory Move
instructions, is loaded into the
indirect I/O or Move instruction, the first two 32-bit opcode fetches is
followed by one or two more 32-bit fetch cycles.
This sample operation describes execution of a SCRIPTS instruction for
a Block Move instruction.
The host CPU, through programmed I/O, gives the
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)
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
Description
Block Move instruction moves data between the SCSI
bus and memory.
I/O or Read/Write instructions cause the LSI53C875A to
trigger common SCSI hardware sequences, or to move
registers.
Transfer Control instruction allows SCRIPTS instructions
to make decisions based on real time SCSI bus
conditions.
Memory Move instruction causes the LSI53C875A to
execute block moves between different parts of main
memory.
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.
DMA Command (DCMD)
Temporary (TEMP)
and DMA Byte
DMA SCRIPTS Pointer
shadow register. In an
DMA SCRIPTS
register causes the
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