; Chapter 2 6811 assembly language programs; Jonathan W. Valvano; This software accompanies the book,; Real Time Embedded Systems published by Brooks Cole;; Program 2.1. Memory allocation places variables in RAM and programs in ROM.; MC68HC11A8      org $0000 ;RAMcnt   rmb 1     ;global      org $B600 ;EEPROMconst fcb 5  ;amount to add      org  $E000 ;ROMinit  ldaa #$FF      staa DDRC ;outputs      clr  cnt        rtsmain  lds  #$00FF ;sp=>RAM      bsr  initloop  ldaa cnt      staa PORTC ;output      adda const      staa cnt      bra  loop      org $FFFE ;ROM      fdb main ;reset vectorProgram 2.5. 6811 assembly implementation of a Mealy Finite State Machine.      org  $B600  Put in EEPROM so it can be changed* Finite State MachineTime  equ  0      Index for time to wait in this stateOut0  equ  1      Index for output pattern if input=0Out1  equ  2      Index for output pattern if input=1Next0 equ  3      Index for next state if input=0Next1 equ  5      Index for next state if input=1IS    fdb  SA     Initial stateSA    fcb  100    Time to wait      fcb  0,0    Outputs for inputs 0,1      fdb  SB     Next state if Input=0      fdb  SD     Next state if Input=1SB    fcb  100    Time to wait      fcb  0,8    Outputs for inputs 0,1      fdb  SC     Next state if Input=0      fdb  SA     Next state if Input=1SC    fcb  15     Time to wait      fcb  0,0    Outputs for inputs 0,1      fdb  SB     Next state if Input=0      fdb  SD     Next state if Input=1SD    fcb  15     Time to wait      fcb  8,8    Outputs for inputs 0,1      fdb  SC     Next state if Input=0      fdb  SA     Next state if Input=1      org $E000      Place assembly program in ROM* 6811 program * Initialization of 6811 and linked structureGO    lds  #$00FF    Initialize stack      ldaa #$08      PC3=output, rest are input      staa $1007     Set DDRC      ldx  IS        Reg X => current state*Linked structure interpreterLL    ldaa Time,X    Time to wait      bsr  WAIT      Reg A is call by value      ldaa $1003      bita #$80      Test input PC7      bpl  is0       Go to is0 if Input=0is1   ldaa Out1,X    Get desired output from linked structure      staa $1003     Set PC3=output      ldx  Next1,X   Input is 1      bra  LLis0   ldaa Out0,X    Get desired output from linked structure      staa $1003     Set PC3=output      ldx  Next0,X   Input is 0      bra  LL        Infinite loop      org  $FFFE      fdb  GO        reset vector; Program 2.8: An assembly subroutine that uses ; comments to delineate its beginning and end.;***************Abs*************************; Input: RegA is signed 8 bit; Output: Reg A is absolute value 0 to 127Abs: tsta     ; already positive?     bpl  ok     negaok   rts* ------------end of Abs -----------------; Program 2.9: Sometimes we can remove a conditional branch and simplify the program.; 6811/6812; uses conditional branchadd16a ldaa u1+1  ;lsb       adda u2+1       staa u3+1       ldaa u1    ;msb       bcc  noc       inca       ;carrynoc    adda u2       staa u3       rts; no conditional branchadd16b ldaa u1+1  ;lsb       adda u2+1       staa u3+1       ldaa u1    ;msb       adca u2       staa u3       rts; Program 2.10: Assembly implementation of a 3 layer software system.***************************High level****************************             org  $E000      ; High level routines start at $F000main:        lds  #$00FF             bsr  Initialize ; simple call to a function in the same layerloop:        bsr  PrintInfo  ; simple call to a function in the same layer             bra  loopInitialize:  ldaa #1       ; function code for InitPrinter             swi           ; call to middle level             rts             org $FFFE     ; high level vector (reset)             fdb  main***************************Middle level****************************             org  $F400    ; Middle level routines start at $F400swihandler:  cmpa #1       ; function code for InitPrinter             bne  notIP             bsr  InitPrinter             bra  swidonenotIP:       cmpa #2       ; function code for PrintInfo             bne  notPI             bsr  PrintInfo             bra  swidonenotPI:                    ; ****errorswidone:     rtiInitPrinter: ldaa #1      ; function code for InitIEEE             ldx  $FF80   ; vector address into the lower level             jsr  0,x     ; call lower level             rts             org  $FFF6    ; middle level vector (SWI)             fdb  swihandler***************************Lower level****************************             org  $F800     ; Lower level routines start at $F800lowhandler:  cmpa #1       ; function code for InitIEEE             bne  notInit             bsr  InitIEEE             bra  lowdonenotInit:     cmpa #2     ; function code for SetDAV             bne  notDAV             bsr  SetDAV             bra  lowdonenotDAV:           ; rest of the functionslowdone:     rtsInitIEEE:         ; lower level implementation, access to hardware             rts             org  $FF80     ; Lower level vector             fdb  lowhandler; Program 2.11: Assembly implementation of SCI initialization.; MC68HC11A8init  ldaa #$33  ;1200 baud      staa BAUD      ldaa #$00  ;mode      staa SCCR1      ldaa #$0C  ;tie=rie=0,       staa SCCR2 ;te=re=1      rts; Program 2.12: Assembly implementation of SCI input.; MC68HC11A8InChar ldaa SCSR   ;status       bita #$20   ;rdrf?       beq  InChar       ldaa SCDR   ;SCI data       rts; Program 2.13: Assembly implementation of SCI output.; MC68HC11A8OutChar ldab SCSR   ;status        bitb #$80   ;tdre?        beq  OutChar           staa SCDR   ;output        rts; Program 2.15: Assembly implementation of input decimal number.; MC68HC11A8 or MC68HC812A4; Input a byte from the SCI ; Inputs:  none; Outputs: Reg B 0 to 255;          C=1 if errorDIGIT    rmb  1       ;globalInUDec   clrb         ;N=0         InUDloop bsr  InChar  ;Next input         bsr  OutChar ;Echo         cmpa #13     ;done if cr         beq  InUDret ;with C=0         cmpa #'0         blo  InUDerr ;error?         cmpa #'9         bhi  InUDerr ;error?         anda #$0F    ;0-9 digit         staa DIGIT         ldaa #10         mul         tsta         ;overflow?         bne  InUDerr          addb DIGIT ;N=10*N+DIGIT         bra  InUDloop InUDerr  ldaa #'?         bsr  OutChar         clrb         sec          ;error flagInUDret  rts; Program 2.16: Assembly implementation of SCI output string.; MC68HC11A8 or MC68HC812A4; Output a string to the SCI ; Inputs:  Reg X points to string;          String ends with 0; Outputs: noneOutString ldaa 0,X          beq  OSdone  ;0 at end          bsr  OutChar          inx          bra  OutString OSdone    rts; Program 2.17: Assembly implementation of SCI output decimal number.; MC68HC11A8 or MC68HC812A4; Output unsigned byte to the SCI ; Inputs:  Reg B= 0 to 255, ;    print as 3 digit ascii; Outputs: none OutUDec  clra    ;Reg D=number         ldx  #100         idiv    ;X=num/100,          xgdx    ;B=100s digit         tba         adda #'0 ;A=100's ascii         bsr  OutCh         xgdx     ;D=num         ldx  #10         idiv     ;X=num/10,         xgdx     ;B=tens digit         tba         adda #'0 ;A=tens ascii         bsr  OutCh         xgdx     ;D=num         tba         adda #'0 ;A=ones ascii         bsr  OutCh         rts