ECE/CS 5780/6780: Embedded System DesignScott R. LittleLecture 3: Assembly Language ProgrammingScott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 1 / 59Administrivia2 versions of CodeWarrior are on the lab machines.You should use the 4.5 version (CW for HC12 v 4.5).Lab 1 was updated yesterday morning.Both team members need to be present for check-off.Lab reports don’t need to be in ”report” format.Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 2 / 59Assembly Language Development ProcessScott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 3 / 59Assembly Language SyntaxLabel Operation Operand CommentPORTA equ $0000 ; Assembly time constantInp ldaa PORTA ; Read data from PORTAIf first character of label is “∗” or “;”, then line is a comment.If first character is white space, then there is no label.Labels composed of characters, digits, “.”, “$”, or “ ”, andmust start with a character, “.”, or “ ”, and are case-sensitive.Labels should be defined only once except those defined by set.With exception of equ and set, a label is assigned value ofprogram counter for the next instruction or assembler directive.A label may have an optional “:” which is ignored or be on aline by itself.Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 4 / 59Assembly Language Syntax (cont)Operations must be proceede d by at least one white spacecharacter, and they are case-insensitive (nop, NOP, NoP).Operations can be an opcode or assembler directive (pseudo-op).Operand must be procee ded by white space.Operands must not contain any white space unless the followingcomment begins with a semicolon.Operands are composed of symb ols or expressions.Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 5 / 59Operand TypesOperand Format Exampleno operand INH clra#<expression> IMM ldaa #4<expression> DIR,EXT,REL ldaa 4<expression>,idx indexed (IND) ldaa 4,x<expr>,#<expr> bit set or clear bset 4,#$01<expr>,#<expr>,< expr > bit test & branch brset 4,#$01,foo<expr>,idx,#<expr>,< expr > bit test & branch brset 4,x,#$01,foo<expression>,idx+ IND, post incr ldaa 4,x+<expression>,idx- IND, post decr ldaa 4,x-<expression>,+idx IND, pre incr ldaa 4,+x<expression>,-idx IND, pre decr ldaa 4,-xacc,idx accum offset IND ldaa A,x[<expression>,idx] IND indirect ldaa [4,x][D,idx] RegD IND indirect ldaa [D,x]Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 6 / 59Indexed Addressing ModeUses a fixed signed offset with a 16-bit register: X, Y, SP, or PC.Offset can be 5-bits, 9-bits, or 16-bits.Example (5-bit):Obj code Op Operand Comment$6A5C staa -4,Y ;[Y-4] = RegAScott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 7 / 59Building the Object Codestaa -4,Y → $6A5CFirst byte is $6A - Op code (pg. 254)Second byte is formatted as %rr0nnnnn (pg. 33).rr is %01 for register Y.nnnnn is %11100 for -4.%0101 1100 → $5C.Information is found in the CPU12 Reference Manual(CPU12RM.pdf).Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 8 / 59Auto Pre/Post Decrement/Increment IndexedCan be used with the X, Y, and SP registers, but not PC.The register used is i ncreme nted/decreme nted by the offset value(1 to 8) either before (pre) or after (p ost) the me mory access.In these examples assume that RegY=2345:Op Operand Commen tstaa 1,Y+ ;Store RegA at 2345, then RegY=2346staa 4,Y- ;Store RegA at 2345, then RegY=2341staa 4,+Y ;RegY=2349, then store RegA at 2349staa 1,-Y ;RegY=2344, then store RegA at 2344Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 9 / 59Building the Object Codestaa 1,X+ → $6A30First byte is $6A - Op code (pg. 254)Second byte is formatted as %rr1pnnnn (pg. 33).rr is %00 for register X.nnnn is %0000 for 1.p is %1 for post.%0011 0000 → $30.Information is found in the CPU12 Reference Manual(CPU12RM.pdf).Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 10 / 59Accumulator Offset IndexedUses two registers, offset is in A, B, or D, while index is in X, Y,SP, or PC.Examples:Op Operand Commen tldab #4ldy #2345staa B,Y ;Store value in RegA at 2349Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 11 / 59Indexed IndirectAdds 16-bit offset to 16-bit register (X,Y,SP, or PC) to computeaddress in which to fetch another address.This second address is used by the load or store.Examples:Op Operand Commen tldy #$2345staa [-4,Y] ;Fetch 16-bit address from $2341,;store $56 at $1234Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 12 / 59Accumulator D Offset Indexed IndirectOffset is in D and index is in another 16-bit register.Computed addressed is used to fetch another address frommemory.Load or store uses the second address.Examples:Op Operand Commentldd #4ldy #$2341stx [D,Y] ;Store value in RegX at $1234Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 13 / 59Load Effective AddressUsed with IND addressing modes.Calculate the effective address and store it in the sp ec ifiedregister: X, Y, or SP.CC bits are not affected.Example:leas -4,SP ;SP -= 4 → $1B9C$1B is leas op code (first byte).Second byte is %rr0nnnnn.%10 is the rr code for SP.%1 1100 is -4.Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 14 / 59Load and Store InstructionsUsed to move data to (from) registers from (to) memory.Load instructions are: ldaa, ldab, ldd, lds, ldx, and ldy.Load addressing modes are: IMM, DIR, EXT, IND.Store instructions are: staa, stab, std, sds, sdx, and sdy.Store addressing modes are: DIR, EXT, IND.CC bits N and Z are updated based on data loaded or stored.Examples:Op Operand Commen tldaa #$FF IMMstaa $25 DIRldab $0025 EXTstd $05,X INDldd $C025 EXTScott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 15 / 59Memory to Memory Move InstructionsUsed to move constant into memory or the value of one memorylocation into another.CC bits are not affected by these i nstructions.Move an 8-bit constant into memory:movb #w,addr [addr]=wMove an 8-bit value memory to memory:movb addr1,addr2 [addr2]=[addr1]Move a 16-bit constant into memory:movw #W,addr {addr}=WMove a 16-bit value memory to memory:movw addr1,addr2 {addr2}={addr1}Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780 16 / 59Clear/Set InstructionsUsed to initialize memory (clr), accumulators (clra,clrb), orbits in the CC (clc, cli, clv).clr addressing modes are: EXT, IND.clra, clrb, clc, cli, clv are INH.Examples:Op Operand Commen tclra INHclr $0025 EXTThe carry (C), interrupt mask (I), and overflow (V) bits in theCC can also be set (sec, sei, sev).Scott R. Little (Lecture 3: Assembly) ECE/CS 5780/6780
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