Connections:-

• The transformer terminals are given to bridge rectifier to generate rectified DC.
• It is filtered and given to regulator IC 7805 to generate 5 V pure DC. LED indicates supply is ON.
• All the push button micro switches J1 to J8 are connected with port P1 as shown to form serial keyboard.
• 12 MHz crystal is connected to oscillator terminals of 89C51 with two biasing capacitors.
• All the LEDs are connected to port P0 as shown
• Port P2 drives stepper motor through current driver chip ULN2003A.
• The common terminal of motor is connected to Vcc and rest all four terminals are connected to port P2 pins in sequence through ULN chip.

Org 00h

          mov r0,#01h     ; initileze key count

          mov p1,#0ffh    ; P1 as input port        

 lop:    mov a,p1

          cjne a,#0ffh,jmp

          ajmp lop           ; loop until any key

                                 ; is pressed

 jmp:     clr p0.0          ; indicates keypress

 loop:    rrc a             

            jnc num          ; get key no.

            inc r0

            sjmp loop

   num: acall dely        ; key debounce delay

            setb p0.0

           cjne r0,#01h,nxt      ; for 1^st key         

           acall clkwise          ; rotate motor  

           sjmp over              ; clock wise 

    nxt:   cjne r0,#02h,over  ; for 2^nd key     

           acall aclkwise        ; rotate anticlock

over:  mov p2,#00h      ; restore initial

         mov p1,#0ffh      ; data and

         mov r0,#01h

         sjmp lop             ; jump to loop again

   clkwise:

         mov r1,#32h       ; load count 50d

    go: clr  p0.1

         mov p2,#01h      ;give 4 pulses in loop

         acall delay         ; total 200 pulses

         mov p2,#02h      ; each coil energized

         acall delay         ; one by on in single

         setb p0.1

         mov p2,#04h      ; coil excitation

         acall delay         ; 30 ms delay in betwn

         mov p2,#08h      ; means speed is

         acall delay         ; 10 RPM

         djnz r1,go

         ret

 aclkwise:

         mov r1,#32h

  go1:clr p0.2

         mov p2,#01h

         acall delay

          mov p2,#08h   ; revert the pulse

         acall delay       ; sequence for

          setb p0.2

         mov p2,#04h   ; anticlockwise

         acall delay

         mov p2,#02h

         acall delay

         djnz r1,go1

          ret

     delay:

         mov r5,#1Eh    ; load count 30

lop2: mov r6,#FAh    ; give 1 ms delay

 lop1:nop                   ; so it gives full

          nop                 ; 30 ms delay

          djnz r6,lop1

          djnz r5,lop2

          ret

      dely:

         mov r5,#0C8h   ; load count 200

lop2: mov r6,#0FAh    ; for 200ms delay

 lop1:nop

          nop

          djnz r6,lop1

          djnz r5,lop2

          ret

 end

Program 2:-
Here in this program we shall limit the motor to rotate only 7.2^o in either direction when the key is pressed. When first key is pressed motor rotates in clockwise direction and when second is pressed anticlockwise direction. LED1 and LED2 indicate the clockwise and anticlockwise rotation.
Note: - In industries this is also known as “jogging” (jog control). This is done to check in which direction motor will start running.
 

Org 00h

          mov r0,#01h   ; initileze key count

          mov p1,#0ffh  ; P1 as input port        

 lop:   mov a,p1

           cjne a,#0ffh,jmp

           ajmp lop        ; loop until any key

                                 ; is pressed

 jmp:     clr p0.0        ; indicates keypress

 loop:    rrc a            

            jnc num         ; get key no.

            inc r0

            sjmp loop

   num: acall dely    ; key debounce delay

            setb p0.0

           cjne r0,#01h,nxt ; for 1^st key         

           acall clkwise    ; rotate motor  

           sjmp over         ; clock wise 

    nxt: cjne r0,#02h,over ; for 2^nd key     

           acall aclkwise   ; rotate anticlock

over:   mov p2,#00h    ; restore initial

           mov p1,#0ffh    ; data and

           mov r0,#01h

           sjmp lop        ; jump to loop again

   clkwise:

         clr p0.1

         mov p2,#01h ;give 4 pulses in loop

         acall delay ; as 1.8^o step resolution    

         mov p2,#02h ; total 7.2^o rotation

         acall delay      ; in single coil

         setb p0.1

         mov p2,#04h  ; excitation

         acall delay  ; 30 ms delay in betwn

         mov p2,#08h; means speed is

         acall delay    ; 10 RPM

          ret

 aclkwise:

         clr p0.1

         mov p2,#01h

         acall delay

          mov p2,#08h ; revert the pulse

         acall delay      ; sequence for

         setb p0.1

         mov p2,#04h  ; anticlockwise

         acall delay

         mov p2,#02h

         acall delay

          ret

     delay:

         mov r5,#1Eh  ; load count 30

lop2: mov r6,#FAh  ; give 1 ms delay

 lop1:nop                  ; so it gives full

          nop                 ; 30 ms delay

          djnz r6,lop1

          djnz r5,lop2

          ret

      dely:

         mov r5,#0C8h ; load count 200

lop2: mov r6,#0FAh ; for 200ms delay

 lop1:nop

          nop

          djnz r6,lop1

          djnz r5,lop2

          ret

 end

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