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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.
6.3.4.1
Program 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.
6.3.4.2
Stack 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.
6.3.4.3
Register 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.
6.3.4.4
Memory 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 FORMATS
INSTRUCTION SET INTRODUCTION
6 - 11
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