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Transfer Control Instructions 5-27
DMA SCRIPTS Pointer Save (DSPS) register. The DSP
register now contains the address of the next instruction.
If the comparisons are false, the LSI53C875A fetches the
next instruction from the address pointed to by the DMA
SCRIPTS Pointer (DSP) register, leaving the instruction
pointer unchanged.
Call Instruction
The LSI53C875A 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 LSI53C875A executes a Call instruction, the
instruction pointer contained in the DSP register is stored
in the Te mpo r ar y ( T EM P) 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 LSI53C875A fetches the
next instruction from the address pointed to by the DSP
register and the instruction pointer is not modified.
Return Instruction
The LSI53C875A 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 DSP
register. The LSI53C875A 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.