LSI LSI53C1000, Technical Manual

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5-28 SCSI SCRIPTS Instruction Set
the DMA SCRIPTS Pointer (DSP) register with the
contents of the DMA SCRIPTS Pointer Save (DSPS)
register. The DSP register now contains the address of
the next instruction.
If the comparisons are false, the LSI53C1000 fetches the
next instruction from the address pointed to by the
DMA
SCRIPTS Pointer (DSP) register, leaving the instruction
pointer unchanged.
When the JUMP64 instruction is used, a third Dword is
fetched and loaded into the
SCRIPT Fetch Selector
(SFS) register. Bit 22 indicates whether the jump is to a
32-bit address (0) or a 64-bit address (1). All
combinations of jumps are still valid for JUMP64.
Call Instruction
The LSI53C1000 can do a true/false comparison of the
ALU carry bit, or compare the phase and/or data as
defined by the Phase Compare, Data Compare, and
True/False bit fields. If the comparisons are true, it loads
the
DMA SCRIPTS Pointer (DSP) register with the
contents of the DMA SCRIPTS Pointer Save (DSPS)
register and that address value becomes the address of
the next instruction.
When the LSI53C1000 executes a Call instruction, the
instruction pointer contained in the
DMA SCRIPTS
Pointer (DSP) register is stored in the Temporary (TEMP)
register. Since the TEMP register is not a stack and can
only hold one Dword, nested call instructions are not
allowed.
If the comparisons are false, the LSI53C1000 fetches the
next instruction from the address pointed to by the
DMA
SCRIPTS Pointer (DSP) register and the instruction
pointer is not modified.
Return Instruction
The LSI53C1000 can do a true/false comparison of the
ALU carry bit, or compare the phase and/or data as
defined by the Phase Compare, Data Compare, and
True/False bit fields. If the comparisons are true, it loads
the
DMA SCRIPTS Pointer (DSP) register with the
contents of the DMA SCRIPTS Pointer Save (DSPS)
register. That address value becomes the address of the
next instruction.