Freescale Semiconductor SC140 specifications Special Addressing Modes

Address Generation Unit

2.3.3.4 Special Addressing Modes

The special addressing modes do not use an address register when specifying an effective address. They either use an immediate value that is included in the instruction for the data value, such as the data value address, or they use a register that is implicitly referenced by the instruction for the data value.

•Immediate Short Data — A 5-bit, 6-bit, or 7-bit operand is part of the instruction operation word. The 5-bit zero-extended operand is used for DALU and AGU arithmetic instructions. The 6-bit zero-extended operand is used for DALU instructions to move short immediate data to an LCn register. The 7-bit sign-extended operand is used for immediate moves to a register. This reference is classified as a program reference. An example is: doen2 #$3f. The value $3f, 63, is loaded to loop counter 2.

•Immediate Word Data — This addressing mode requires a one-word instruction extension. The immediate data is a 16-bit operand. This reference is classified as a program reference. An example is: doen2 #$40. The value 64 is loaded to loop counter 2. The value exceeds the 6-bit limit for immediate short data, so an extra word is needed for the encoding.

•Immediate Long Data — This addressing mode requires a two-word instruction extension. The immediate data is a 32-bit operand. This reference is classified as a program reference. An example is: move.l #$f00d0d01,n0. The 32-bit unsigned value is moved to the general register n0.

•Absolute Word Address — This addressing mode requires a one-word instruction extension. The operand address occupies 16 bits in the instruction operation words, and is zero-extended to form a 32-bit address. This reference is classified as a memory reference. An example is: move.w ($8a20),d0.

•Absolute Long Address — This addressing mode requires a two-word instruction extension. A 32-bit address is contained in the instruction words. This reference is classified as a memory reference. An example is: move.w ($34008a20),d0.

•Absolute Jump Address — The operand occupies 32 bits in the instruction operation words. It requires a two-word instruction extension. This reference is classified as a program reference. An example is: jmp lbl4, where the instruction is encoded with the program memory address of lbl4.

•Implicit Reference — Some instructions make implicit reference to the PC, normal or exception stack, loop registers (SA0, SA1, SA2, SA3, LC0, LC1, LC2, LC3), or status register (SR). These registers are implied by the instruction, and their use is defined by the individual instruction descriptions. An example is: tfra osp,r2, which transfers the 32-bit word stored at the other (non-active) stack pointer to address register R2.

SC140 DSP Core Reference Manual 2-41