Motorola DSP56000 Special Addressing Modes, Immediate Data, Absolute Address, Immediate Short

INSTRUCTION FORMATS

6.3.5.3Special Addressing Modes

The special addressing modes do not use specific registers to specify an effective address. These modes specify the operand or the operand address in a field of the instruction, or they implicitly reference an operand. Figure examples are given for each of the special addressing modes discussed in the following paragraphs.

6.3.5.3.1Immediate Data

Classified as a program reference, this addressing mode requires one word of instruction extension containing the immediate data. Figure 6-7shows three examples. Example A moves immediate data to register A0 without affecting A1 or A2. Examples B and C zero fill register A0 and sign extend register A2.

6.3.5.3.2Absolute Address

This addressing mode requires one word of instruction extension containing the absolute address. Figure 6-8shows that MOVE Y:$5432,B0 copies the contents of address $5432 into B0 without changing memory location $5432, register B1, or register B2. This addressing mode is classified as both a memory reference and program reference. The 16-bit absolute address is stored in the 16 LSBs of the extension word; the eight MSBs are zero filled.

6.3.5.3.3Immediate Short

The 8- or 12-bit operand, which is in the instruction operation word, is classified as a pro- gram reference. The immediate data is interpreted as an unsigned integer (low-order portion) or signed fraction (high-order portion), depending on the destination register. Fig- ure 6-9shows the use of immediate short addressing in four examples.

6.3.5.3.4Short Jump Address

The operand occupies 12 bits in the instruction operation word, which allows addresses $0000–$0FFF to be accessed (see Figure 6-10). The address is zero extended to 16 bits

MOTOROLA INSTRUCTION SET INTRODUCTION 6 - 15