hello

                
;--------------------------VARIABLES USED-----------------------------------------

LEFT_WORD       EQU     1100B   ; when written to port2,will turn robo to left.
RIGHT_WORD      EQU     0011B   ; when written to port2,will turn robo to right.
FWD_WORD        EQU     1010B   ; when written to port2,will move robo in forward direction.
REV_WORD        EQU     0101B   ; when written to port2,will move robo in reverse direction.
STOP_WORD       EQU     1111B   ; when written to port2,will stop the robo.
SPEED           EQU     R0      ; used to hold the speed of the robo;
DIRECT1         EQU     30H     ; internal RAM location used for genrating PWM.
DIRECT2         EQU     31H     ; internal RAM location used for genrating PWM.
TEMP            EQU     117D    ; used delay generation in PWM.

;---------------------------------------------------------------------------------------------
                ORG             000H
                SJMP    RESET_VECTOR    ;

; ------------------------EXTERNALINTERRUPT-------------------------------------
                ORG     0003H
                SJMP    EXT_INT         ;
;---------------------------------------------

ORG     032H
                
RESET_VECTOR:   MOV     IE, #10000001B  ;enable external interrupt
                CLR     C               ;
                MOV     SPEED, #0001H   ; initialize speed with 1
                SJMP    FIND_SPEED      ;
;----------------------------------------------------------------------------------
ORG     060H

EXT_INT:        MOV     A, P1           ; read port1 to accumulator

TEST_STOP:      CJNE    A, #11111111B, TEST_LEFT        ;
                SJMP    STOP            ;

TEST_LEFT:      CJNE    A, #11110111B, TEST_RIGHT       ;
                SJMP    LEFT            ;

TEST_RIGHT:     CJNE    A, #11111011B, TEST_REV ;
                SJMP    RIGHT           ;

TEST_REV:       CJNE    A, #11111101B, TEST_FWD ;
                SJMP    REV             ;

TEST_FWD:       CJNE    A, #11111110B, TEST_INCSPEED    ;
                SJMP    FWD             ;

TEST_INCSPEED:  CJNE    A, #11111100B, TEST_DECSPEED    ;
                SJMP    INCSPEED        ;

TEST_DECSPEED:  CJNE    A, #11110011B, TEST_STOP        ;
                SJMP    DECSPEED        ;
;----------------------------------------------------------------

STOP:           MOV     P2, #STOP_WORD  ; stops the robo
                SJMP    PWM             ;

LEFT:           MOV     P2, #LEFT_WORD  ; turns robo to left
                SJMP    PWM             ;

RIGHT:          MOV     P2, #RIGHT_WORD ; turns robo to right
                SJMP    PWM             ;

REV:            MOV     P2, #REV_WORD   ; moves robo in reverse direction
                SJMP    PWM             ;

FWD:            MOV     P2, #FWD_WORD   ; moves robo in forward direction
                SJMP    PWM             ;
INCSPEED:       INC     SPEED           ; increase the speed    
                SJMP    FIND_SPEED      ;

DECSPEED:       DEC     SPEED           ; decrease the speed
                SJMP    FIND_SPEED      ;
;------------------finds the speed -----------------------------------------------
FIND_SPEED:
                CJNE    SPEED, #4H, FAIL1       ;
                SJMP    SPEED4                  ;
FAIL1:          CJNE    SPEED, #3D, FAIL2       ;
                SJMP    SPEED3                  ;
FAIL2:          CJNE    SPEED, #2D, FAIL3       ;
                SJMP    SPEED2                  ;
FAIL3:          CJNE    SPEED, #1D, FAIL4       ;
                SJMP    SPEED1                  ;
FAIL4:          CJNE    SPEED, #0D, FAIL5       ;
                MOV     SPEED, #1D              ;
                SJMP    FIND_SPEED              ;
FAIL5:          MOV     SPEED, #4D              ;
                SJMP    FIND_SPEED              ;

;----------- turns on LEDs to indicate the speed and loads registers with delay -------------

SPEED4:         MOV     P0, #11110111B  ;
                SJMP    $               ;

SPEED3:         MOV     DIRECT1, #255D  ;
                MOV     DIRECT2, #2D    ;
                MOV     P0, #1011B      ;
                SJMP    PWM             ;

SPEED2:         MOV     DIRECT1, #130D  ;
                MOV     DIRECT2, #127D  ;
                MOV     P0, #1101B      ;
                SJMP    PWM             ;

SPEED1:         MOV     DIRECT1, #5D    ;
                MOV     DIRECT2, #252D  ;
                MOV     P0, #1110B      ;
                SJMP    PWM             ;

;----------------generates PWM on pin P3.0---------------------------------------------------

PWM:
                MOV     R1, DIRECT1     ;
                MOV     R2, DIRECT2     ;
                CPL     P3.0            ;
LOOP1:          DJNZ    R1, LOOP1       ;
                MOV     R1, #TEMP       ;

LOOP2:          DJNZ    R1, LOOP2       ;
                CPL     P3.0            ;
LOOP3:          DJNZ    R2, LOOP3       ;
                MOV     R2, #TEMP       ;
LOOP4:          DJNZ    R2, LOOP4       ;
                SJMP    PWM             ;
END
;----------------end of the code--------------------------------------------