Connect a push button switch to P3.4 and an 8 Ohm speaker to P1.0 as shown below

Question

Connect a push button switch to P3.4 and an 8 Ohm speaker to P1.0 as shown below. The 2N5307 is a Darlington transistor pair which has a current gain of beta > 2000 and its collector current can be up to 1.2 amps. If you output a square wave on P1.0 at frequency f_o you will hear a tone on the speaker with a base frequency f_o, plus odd harmonic overtones. For this assignment write the assembly-code to output an A-note (about 440Hz) in response to the push button on P3.4. Your assembly code must contain a subroutine which does the software time delay and a macro which output a bit to P3.4.

Explanation / Answer

lets consider frequency of external oscillator be 12MHz

so the timers will run at 1MHz ,time period = 1/1MHz= 1microsecond           (timer clock frequency = XTAL/12)

A-note frequeny =440Hz , timeperiod = 1/440=2272.7microseconds

duty ratio will be 50% so timer count=(2272.7micros/1micros)*1/2=1136.35    approx=11136 =470H

value to be loaded in Timer register=FFFFH-470H+1 =FB8FH   

Therefore TH=FBH     ,TL=8FH

Since P3.4 is configured to be Active low (Gives 0 as Input to P3.4 When button is Pushed )

code:

MOV P1,#00000000B                                 //Initializing P1.0 as Output

MOV P3,#00010000B                                //Initializing P3.4 as Input

MOV TMOD,#00000001B // Sets Timer 0 to MODE1 (16 bit timer)

MOV TH0,#0FBH                  // Loads TH0 register with FBH

MOV TL0,#08FH                  // LOads TL0 register with 8FH

MAIN: MOV C,P3.4 //Load C with P3.4 value (1 if off and 0 if on)

          JB C,MAIN                                                   // If C=1, goes to main,else goes forward

          ACALL DELAY                                                //Calling Delay Subroutine and waits for half time period

      SETB P1.0                                                    //Makes P1.0 high

          ACALL DELAY                                               // waits for half time period

          CLR P1.0                                                     //Makes P1.0 low

          SJMP MAIN

DELAY:                 

             SETB TR0                           // Starts the Timer 0

HERE: JNB TF0,HERE                       // Loops here until TF0 is set (ie;until roll over)

           CLR TR0                              // Stops Timer 0

           CLR TF0                             // Clears TF0 flag

           RET

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