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MSP430 Assembly Language Overview

Explore MSP430 Assembly language features, instruction sets, and register structures. Learn about addressing modes, constant generators, and groups of instructions in detail.

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MSP430 Assembly Language Overview

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  1. ECE 447 Fall 2009 Lecture 4: TI MSP430 Architecture and Instruction Set

  2. ECE447: MSP430 Assembly language • Specific to the platform (ie: The MSP430). • No data types, structures, or explicit execution control (for, while, if, switch) • Define locations for and variables and program code. • No complex instructions, such as long integer math, floating point. • Close coupling to the hardware (registers, peripherals and input/output ports) • Teaches a more in depth appreciation for the device architecture.

  3. ECE 447: Levels of Software High-level language (C, C++, Pascal) compiler Assembly language (MSP430, 8051, Z80) assembler Object code linker Machine language

  4. ECE 447: Levels of Software C Pascal compiler Pseudocode MSP430 8051 Z80 assembler Object code Object code Object code linker Machine language Machine language Machine language

  5. ECE447: Assembly vs. Machine code for the MSP430 mov.w R5, R6 ; 4506 – Machine code translation • Opcode (4 bits): • Operation Code • S-reg and Dreg (4 bits each): • Specifies CPU registers associated with the src and dst • Ad (1 bit): • Gives mode of addressing for dst • B/W (1 bit): • chooses whether the operand is a byte (1) or a word (0) • As (2 bits): • gives the mode of addressing for the src

  6. ECE 447: Features of Assembly Language 1. Very hardware dependent 2. Not very portable (if at all) 3. Very detailed (responsible for all register contents) 4. No inherent data types 5. Requires programming discipline 6. Difficult to document 7. Access to all hardware intricacies of the chip 8. Fastest execution 9. Small memory usage

  7. ECE447: MSP430 Register Structure PC: Program Counter • Contains the address of the next instruction to be executed. SP: Stack Pointer • Contain the address of the stack frame. The stack is primarily responsible for storing the return address of subroutine calls. SR: Status Register • Contains a set of flags CG1/CG2: Constant Generator • Provides the six most frequently used values so that they do not need to be fetched from memory.

  8. ECE 447: MSP430 Status Register (SR) • V - Overflow, set when a result of a signed operation has overflowed. • N - Negative, set to the msb of the result which indicates a negative number if the values are signed. • Z - Zero, set when the result is 0. • C - Carry, set to indicate an arithmetic operation is too larger to fit in the destination space. • GIE - General Interrupt Enable - Set to enable the maskable interrupts. • OSCOFF, CPUOFF, SCG0, SCG1 - bits to control the mode of operation of the MCU. Will be covered in detail in discussion of Low Power Modes.

  9. ECE447: Groups of Instructions (1) • Movement - general (mov) • Movement - stack (push, pop) • Arithmetic • i. One Operand (clr, dec, inc, test) • ii. Two Operands (add, sub, cmp) • iii. Decimal Arithmetic (dadd, dadc) • Logic Instructions • i. One Operand (inv(ert)) • ii. Two Operands (and, xor, bis, bic)

  10. ECE447: Groups of Instructions (2) • Status Register Instructions • clr(c/z/n): clear specified bits • set(c/z/n): set specified bits • dint/eint: disable/enable interrupts • Shift and Rotates • rla, rra: arithmetic shift left/right • rlc, rrc: rotate through carry left/right • Byte Manipulation • swpb: swap bytes (word only) • sxt: sign extend (word only)

  11. ECE447: Groups of Instructions (3) • Flow Control Operations • br: branch (go to) • call: call a subroutine • ret: return from subroutine • reti: return from interrupt • nop: no operation (consumes one cycle) • Jumps • jmp: unconditional jump • conditional jmp’s: various conditional jumps

  12. ECE447: MSP430 Operand width notation • Most MSP430 instructions can operate on either 8 or 16 bit data. • In MSP430X device the 20 bit address bus is also supported for operands. • The move instruction: • mov.b - Operands will be byte wide • mov.w - Operands will be word (16-bit) wide • mov.a - Operands will be address word (20-bit) wide

  13. ECE447: Move Instruction (mov) • Only one mov instruction to move data • Can address all of memory as either source or destination, including all registers. • Note: The MSP430 mov instruction does not affect the SR register bits.

  14. Addressing Modes The ways in which operands can be specified

  15. Register Mode

  16. Indexed Mode

  17. Indexed Mode (cont.)

  18. Symbolic Mode

  19. Symbolic Mode (cont.)

  20. Absolute Mode

  21. Absolute Mode (cont.)

  22. Indirect Register Mode

  23. Indirect Register Mode (cont.)

  24. Indirect Autoincrement Mode

  25. Indirect Autoincrement Mode (cont.)

  26. Immediate Mode

  27. Immediate Mode (cont.)

  28. Addressing Mode Summary

  29. Addressing Mode Examples

  30. ECE447: MSP430 Constant Generator and Emulated Instruction • Two registers in the MSP430 allow up to 7 common constant values. • R3/CG2 and R2/SR/CG1 when accessed in various addressing modes provide “0” base for absolute addressing and six immediate values 0,1,2,4,8, and 0xFFFF. • The instruction that use these values are “emulated,” that is no actual machine instruction exists for the mnemonic

  31. ECE447: MSP430 Constant Generator and Emulated Instruction InstructionExplanationEmulation nop No operation commenced mov R3, R3

  32. Summary • Assembly Rocks! • MSP430 Registers • Instruction Types • The mov command • Addressing Modes

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