LSI LSI53C896, Technical Manual

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5-28 SCSI SCRIPTS Instruction Set
When the JUMP64 instruction is used, a third Dword is
fetched and loaded into the
SCRIPTS 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 LSI53C896 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 LSI53C896 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 LSI53C896 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 LSI53C896 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.
When a Return instruction is executed, the value stored
in the
Temporary (TEMP) register is returned to the DMA
SCRIPTS Pointer (DSP) register. The LSI53C896 does
not check to see whether the Call instruction has already
been executed. It does not generate an interrupt if a
Return instruction is executed without previously
executing a Call instruction.
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