Subversion Repositories RISCMCU

; This program is for simulation purpose
; It demo how the MCU output 3, 2 and 1 to each port (Port B, Port C and Port D)
; There are 3 approaches used in accomplishing the above task

.include "riscmcu.inc"

.def    B = r16
.def    C = r17
.def    D = r18
.def    TEMP = r19



        rjmp    reset           ; reset vector
        ret                     ; external interrupt vertor(not use)
        ret                     ; timer overflow interrupt vertor (not use)


reset:
        clr     TEMP            ; r19 = 00
        com     TEMP            ; r19 = FF
        out     DDRB,TEMP       ; set all Port B pins as output
        out     DDRC,TEMP       ; set all Port C pins as output
        out     DDRD,TEMP       ; set all Port D pins as output



; Approach 1, output to Port B

        ldi     B,3             ; r16 = 03
again1: out     PORTB,B         ; Port B now output 03
        dec     B               ; r16 = r16 - 1
        cpi     B,0             ; if r16 = 0,
        brne    again1          ;   branch to again1
                                


; Approach 2, output to Port C

        clr     TEMP            ; r19 = 00
        inc     C               ; r17 = 01
        inc     C               ; r17 = 02
        inc     C               ; r17 = 03
again2: out     PORTC,C         ; Port C now output 03
        subi    C,1             ; r17 = r17 - 1
        cpse    C,TEMP          ; if r17 != r19 (means if r17 != 0),
        rjmp    again2          ;    branch to again2
                                


; Approach 3, output to Port D

        clr     D               ; r18 = 00
        subi    D,-3            ; r18 = r18 - (-3) = 03
again3: out     PORTD,D         ; Port D now output 03
        dec     D               ; r18 = r18 -1
        in      TEMP,SREG       ; transfer the value of SR to R19
        sbrs    TEMP,1          ; if bit 1 in R19 (the Z-flag) is set, skip the next instruction
        rjmp    again3          ;    else branch to again3
                                


end:    rjmp    end             ; Branch Forever
        sei                     ; (Set I-Bit in SR) This 2 instructions won't execute 
        set                     ; (Set T-Bit in SR)   even they are fetched to the IR