Motorola DSP56000, 24-Bit Digital Signal Processor manual YX Memory References, Addressing Modes

INSTRUCTION FORMATS

6.3.4.4.2Y Memory References

The operand, a word reference, is in Y memory space. Data can be transferred from mem- ory to a register or from a register to memory.

6.3.4.4.3L Memory References

Long (L) memory space references both X and Y memory spaces with one operand address. The data operand is a long-word reference developed by concatenating the X and Y memory spaces (X:Y). The high-order word of the operand is in the X memory; the low-order word of the operand is in the Y memory. Data can be read from memory to con- catenated registers X1:X0, A1:A0, etc. or from concatenated registers to memory.

6.3.4.4.4YX Memory References

XY memory space references both X and Y memory spaces with two operand addresses. Two independent addresses are used to access two word operands – one word operand is in X memory space, and one word operand is in Y memory space. Two effective addresses in the instruction are used to derive two independent operand addresses – one operand address may reference either X or Y memory space and the other operand address must reference the other memory space. One of these two effective addresses specified in the instruction must reference one of the address registers, R0–R3, and the other effective address must reference one of the address registers, R4–R7. Addressing modes are restricted to no-update and post-update by +1, –1, and +N addressing modes. Each effective address provides independent read/write control for its memory space. Data may be read from memory to a register or from a register to memory.

6.3.5 Addressing Modes

The DSP instruction set contains a full set of operand addressing modes. To minimize execution time and loop overhead, all address calculations are performed concurrently in the address ALU.

Addressing modes specify whether the operand(s) is in a register or in memory, and pro- vide the specific address of the operand(s). An effective address in an instruction will specify an addressing mode, and, for some addressing modes, the effective address will further specify an address register. In addition, address register indirect modes require additional address modifier information that is not encoded in the instruction. The address modifier information is specified in the selected address modifier register(s). All indirect memory references require one address modifier, and the XY memory reference requires two address modifiers. The definition of certain instructions implies the use of specific reg- isters and addressing modes.

MOTOROLA INSTRUCTION SET INTRODUCTION 6 - 13