###


ORG 00H 
MOV DPTR,#SSDisplay // moves the address of LUT to DPTR
MOV P1,#00000000B  // sets P1 as output port
MOV P0,#00000000B  // sets P0 as output port
CLR P3.0  // sets P3.0 as output for sending trigger
SETB P3.1  // sets P3.1 as input for receiving echo
MOV TMOD,#00100000B  // sets timer1 as mode 2 auto reload timer
MAIN: MOV TL1,#210D  // loads the initial value to start counting from
      MOV TH1,#210D  // loads the reload value
      MOV A,#00000000B  // clears accumulator
      SETB P3.0  // starts the trigger pulse
      ACALL DELAY1  // gives 10uS width for the trigger pulse
      CLR P3.0  // ends the trigger pulse
HERE: JNB P3.1,HERE // loops here until echo is received
BACK: SETB TR1  // starts the timer1
HERE1: JNB TF1,HERE1 // loops here until timer overflows (ie;48 count)
      CLR TR1  // stops the timer
      CLR TF1  // clears timer flag 1
      INC A  // increments A for every timer1 overflow
      JB P3.1,BACK // jumps to BACK if echo is still available
      MOV R4,A // saves the value of A to R4
      ACALL DLOOP  // calls the display loop
      SJMP MAIN  // jumps to MAIN loop
 
DELAY1: MOV R6,#2D  // 10uS delay
LOOP1: DJNZ R6,LOOP1
RET     
 
DLOOP: MOV R5,#50D  // loads R5 with 100D
BACK1: MOV A,R4 // loads the value in R4 to A
       MOV B,#100D  // loads B with 100D
       DIV AB    // isolates the first digit
       SETB P1.0  // activates LED display unit D1
       ACALL DISPLAY  // calls DISPLAY subroutine
       MOV P0,A // moves digit drive pattern for 1st digit to P0
       ACALL DELAY    // 1mS delay
       ACALL DELAY
       MOV A,B  // moves the remainder of 1st division to A
       MOV B,#10D  // loads B with 10D
       DIV AB    // isolates the second digit
       CLR P1.0  // deactivates LED display unit D1
       SETB P1.1  // activates LED display unit D2
       ACALL DISPLAY
       MOV P0,A // moves digit drive pattern for 2nd digit to P0
       ACALL DELAY
       ACALL DELAY
       MOV A,B // moves the remainder of 2nd division to A
       CLR P1.1  // deactivates LED display unit D2
       SETB P1.2  // activates LED display unit D3
       ACALL DISPLAY
       MOV P0,A // moves the digit drive pattern for 3rd digit to P0
       ACALL DELAY
       ACALL DELAY
       CLR P1.2  // deactivates LED display unit D3
       DJNZ R5,BACK1 // repeats the display loop 100 times
       RET
 
DELAY: MOV R7,#250D   // 1mS delay
LABEL2: DJNZ R7,LABEL2
        RET
 
DISPLAY: MOVC A,@A+DPTR  // gets the digit drive pattern for the content in A
         RET
 
SSDisplay:  DB 0C0H // Hex code to display DISPLAY 0
DB 0F9H // DISPLAY 1
DB 0A2H // DISPLAY 2
3
										

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Filed Under: 8051 Microcontroller, Electronic Projects, Tech Articles
Tagged With: 8051, at89s52, distance finder, hc-sr04, ultasonic sensor