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Microcontroller Assembly Programming Guide

Learn the top assembly instructions, data organization, and programming concepts for microcontroller design using HCS12.

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Microcontroller Assembly Programming Guide

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  1. ECE 372 – Microcontroller DesignAssembly Programming • HCS12 Assembly Programming • Basic Assembly Programming • Top Assembly Instructions (Instruction You Should Know!) • Assembly Programming Concepts • Data Organization

  2. ECE 372 – Microcontroller DesignAssembly Programming • HCS12 Assembly Instructions • Load and Store Instructions • Arithmetic Operations • Logic Operations • Branch Instructions • Shift and Rotation Operation • Bit tests and Bit manipulations • Stack and Index Pointer Operations • Condition Code Register Instructions • Subroutine Calls • Interrupt Handling Operations • Miscellaneous Operations

  3. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Load and Store Instructions • ldaa/ldab/ldd - Load A/B/D from memory (or immediate value) • ldx/ldy - Load Index Register X/Y from memory (or immediate value) • lds - Load Stack Pointer (SP) from memory (or immediate value) • staa/stab/std - Store A/B/D to memory • stx/sty – Store Index Register X/Y to memory • sts – Store Stack Pointer (SP) to memory

  4. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Arithmetic Operations • adda/addb/addd – Add memory (or immediate value) to A/B/D • suba/subb/subd – Subtract memory (or immediate value) from A/B/D • aba – Add B to A • sba – Subtract B from A • inca/incb/inx/iny – Increment A/B/X/Y • e.g. A = A + 1 • deca/decb/dex/dey – Decrement A/B/X/Y • e.g. A = A - 1

  5. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Arithmetic Operations • cmpa/cmpb/cpd/cpx/cpy – Compare A/B/D/X/Y with memory (or immediate value) • Branch follows (e.g. greater, less, equal) • mul – Performs 8-bit unsigned multiplication of A and B, storing 16-bit result in D • e.g. D = A * B • idiv – Performa 16-bit unsigned division of D and Y, storing quotient in X and remainder in D • e.g. X = D / X and D = D % X

  6. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Logic Operations • anda/andb – Perform 8-bit logical AND of A/B with memory (or immediate value) • oraa/orab – Perform 8-bit logical OR of A/B with memory (or immediate value) • eora/eorb – Perform 8-bit logical XOR of A/B with memory (or immediate value) • bset/bclr – Set/Clear bit in memory using provided mask • bita/bitb – Performs 8-bit logical AND of A/B with memory (or immediate value) and modifies CCR • Contents of A/B or the memory location are not affected

  7. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Branch Instructions (Unsigned/Signed) • beq – Branch if equal (Relative PC Addressing) • bne – Branch if not equal (Relative PC Addressing) • bra – Branch always (Relative PC Addressing) • jmp – Branch always (Absolute Addressing)

  8. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Branch Instructions (Unsigned) • bhi – Branch if higher (Relative PC Addressing) • i.e. unsigned greater than • bhs – Branch if higher or same (Relative PC Addressing) • i.e. unsigned greater than or equal • blo – Branch if lower (Relative PC Addressing) • i.e. unsigned less than • bls – Branch if lower or same (Relative PC Addressing) • i.e. unsigned less than or equal

  9. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Branch Instructions (Signed) • bgt – Branch if greater than (Relative PC Addressing) • bge – Branch if greater than of equal (Relative PC Addressing) • blt – Branch if less than (Relative PC Addressing) • ble – Branch if less than or equal (Relative PC Addressing) • bmi – Branch if minus (Relative PC Addressing) • i.e. negative result • bpl – Branch if plus (Relative PC Addressing) • i.e. positive result

  10. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Long Branch Instructions • Similar to other branch instructions • PC relative addressing • But with 16-bit relative address • Few Examples: • lbra – Branch always (Long Relative PC Addressing) • lbeq – Branch if equals (Long Relative PC Addressing) • lbgt – Branch if greater than (Long Relative PC Addressing)

  11. C 7 6 5 4 3 2 1 0 Rotate Left: ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Shift and Rotate Operations • rola/rolb – Rotate left A/B through carry (C) • rora/rorb – Rotate right A/B through carry (C)

  12. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Shift and Rotate Operations • lsla/lslb/lsld – Logical shift left A/B/D into carry (C) • Same as asla/aslb/asld instructions • Least significant bit is loaded with 0 • Also performs multiply by 2 • lsra/lsrb/lsrd – Logical shift right A/B/D into carry (C) • NOT the same asra/asrb/asrd • Most significant bit is loaded with 0 • Also performs unsigned divide by 2 C 7 6 5 4 3 2 1 0 0 Logical Shift Left: 7 6 5 4 3 2 1 0 C 0 Logical Shift Right:

  13. ECE 372 – Microcontroller DesignAssembly Programming – Top Assembly Instructions • Shift and Rotate Operations • asla/aslb/asld – Arithmetic shift left A/B/D into carry (C) • Same as lsla/lslb/lsld instructions • Least significant bit is loaded with 0 • Also performs multiply by 2 • asra/asrb/asrd – Arithmetic shift right A/B/D into carry (C) • NOT the same lsra/lsrb/lsrd • Most significant bit is loaded with previous most significant bit value • Also performs unsigned/signed divide by 2 7 6 5 4 3 2 1 0 C Arithmetic Shift Right:

  14. If Cond. cond If Body !cond ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts If-Then C Code: if(cond) { // if body } If-Then Assembly Template: cmp?? ; If Cond. b?? EndIf ; Branch !cond ; If Body EndIf:

  15. If Cond. A>=20 If Body !(A>=20) ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts If-Then C Code: if(a>=20) { // if body } If-Then Assembly Code: cmpa, #20 ; If Cond. (A>=20) blo EndIf ; Branch !(A>=20)=>(A<20) ; If Body EndIf:

  16. If–Else Cond. cond !cond If Body Else Body ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts If-Then-Else C Code: if(cond) { // if body } else { // else body } If-Then-Else Assembly Template: cmp?? ; If-Else Cond. b?? Else ; Branch !cond ; If Body bra EndIf ; Branch EndIf Else: ; Else Body ; EndIf:

  17. If–Else Cond. A>=20 !(A>=20) If Body Else Body ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts If-Then-Else C Code: if(a>=20) { // if body } else { // else body } If-Then-Else Assembly Code: cmpa, #20 ; If-Else Cond. (A>=20) blo Else ; Branch !(A>=20)=>(A<20) ; If Body bra EndIf ; Branch EndIf Else: ; Else Body ; EndIf:

  18. Loop Init. Loop Iter. Loop Body Loop Cond. cond !cond ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts For Loop C Code: for(init; cond; iter) { // loop body } For Loop Assembly Template: ?? ; Loop Init. Loop: cmp?? ; Loop Cond. b?? EndLoop ; Branch !cond ; Loop Body ?? ; Loop Iter. bra Loop ; Repeat Loop EndLoop:

  19. J=0 J++ Loop Body Loop Cond. J<10 !(J<10) ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts For Loop C Code: for(J=0; J<10; J++) { // loop body } For Loop Assembly Code: ldaa #0 ; Loop Init. (J=0) Loop: cmpa #10 ; Loop Cond. (J<10) bge EndLoop ; Branch !(J<10)=>(J>=10) ; Loop Body adda #1 ; Loop Iter. (J++) bra Loop ; Repeat Loop EndLoop:

  20. Loop Body Loop Cond. cond !cond ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts While Loop C Code: while(cond) { // loop body } While Loop Assembly Template: Loop: cmp?? ; Loop Cond. b?? EndLoop ; Branch !cond ; Loop Body bra Loop ; Repeat Loop EndLoop:

  21. Loop Body Loop Cond. i!=0 !(i!=0) ECE 372 – Microcontroller DesignAssembly Programming – Programming Concepts While Loop C Code: while(i!=0) { // loop body } While Loop Assembly Code: Loop: cmpa, #0 ; Loop Cond. (i!=0) beq EndLoop ; Branch !(i!=0)=>(i==0) ;Loop Body bra Loop ; Repeat Loop EndLoop:

  22. ECE 372 – Microcontroller DesignAssembly Programming – Data Organization • Data Organization • Global Variables • Constants • Program Code • Local Variables • Return Addresses • Temporary Data

  23. ECE 372 – Microcontroller DesignAssembly Programming – Data Organization • Data Organization • Heap • Block of memory for allocating storage whose lifetime is not related to the execution of the current routine • Often used for dynamically allocated data (malloc) • Typically located at lowest memory address after global varaibles

  24. ECE 372 – Microcontroller DesignAssembly Programming – Data Organization • Data Organization • Stack • Generally – A data structure supporting two basic operations, push and pop • Push – Adds an item to the top of the stack • Pop – Removes an item from the top of the stack • LIFO – Last In First Out data structure (opposite of queue) • Stack Pointer (SP) • Points to memory location corresponding to the top of the stack • Must be initialized within your assembly program

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