Motorola DSP56000 Operand References, Program References, Stack References, Register References

INSTRUCTION FORMATS

D[n]	Bit n of D Affected
r	Rounding Constant
I1,I0	Interrupt Priority Level in SR
LF	Loop Flag in SR

6.3.4 Operand References

The DSP separates operand references into four classes: program, stack, register, and memory references. The type of operand reference(s) required for an instruction is spec- ified by both the opcode field and the data bus movement field of the instruction. However, not all operand reference types can be used with all instructions. The operand size for each instruction is either explicitly encoded in the instruction or implicitly defined by the instruction operation. Implicit instructions support some subset of the five operand sizes.

6.3.4.1Program References

Program (P) references, which are references to 24-bit-wide program memory space, are usually instruction reads. Instructions or data operands may be read from or written to pro- gram memory space using the move program memory (MOVEM) and move peripheral data (MOVEP) instructions. Depending on the address and the chip operating mode, pro- gram references may be internal or external memory references.

6.3.4.2Stack References

Stack (S) references, which are references to the System Stack (SS), a separate 32-bit- wide internal memory space, are used implicitly to store the PC and SR for subroutine calls, interrupts, and returns. In addition to the PC and SR, the LA and LC registers are stored on the stack when a program loop is initiated. S references are always implied by the instruction. Data is written to the stack memory to save the processor state and is read from the stack memory to restore the processor state. In contrast to S references, refer- ences to SSL and SSH are always explicit.

6.3.4.3Register References

Register (R) references are references to the data ALU, AGU, and program control unit registers. Data can be read from one register and written into another register.

6.3.4.4Memory References

Memory references, which are references to the 24-bit-wide X or Y memory spaces, can be internal or external memory references, depending on the effective address of the operand in the data bus movement field of the instruction. Data can be read or written from any address in either memory space.

MOTOROLA INSTRUCTION SET INTRODUCTION 6 - 11