Write the main background loop and all required set up code to configure and ena

Question

Write the main background loop and all required set up code to configure and enable an IRQ-not interrupt. Then write an IRQ-not service routine that manipulates a counter called IRQCOUNT, delays for 1/2 second, then returns. Each time an interrupt event occurs (press of pushbutton), the counter should count up by 1. When the counter reaches 17, the counting direction should reverse (count down) until it reaches 0, then it should count up again, and continue this up down functionality. Test your code by wiring a pushbutton switch from the MCUSLK board to the IRQ-not input. The switches on the MCUSLK already have pull-up resistor installed as shown on the drawing below. Set a break point at the IRQ ISR and step through the logic (step over the delay) to make sure everything is working properly. Use the debugger software to monitor the value in IRQCOUNT as the switch is pressed. Remove breakpoints and watch the counter. which should change each time the switch is pressed. Note any inconsistencies in the sequence then note the current setting of the IRQ edge/level bit and change it. Compile and run the code again. Does the edge/level bit have an effect on the counting sequence? Does delay time have an effect on the counting sequence?

Explanation / Answer

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ORG C000 ;set PC to $C000

   Entry:

            ; do some initialization

            movb    #input, porth_ddr        ; set Port H to input

            movb    #output, portb_ddr        ; set Port B to output

            jsr    DELAY

loop:       movb    #ledsoff, portb             ; turn LEDs off

               ldd    #$0                ; initialize Port D

sw2:       brset    porth, #sw2on, sw3         ; if bit 3 Port H high, branch to sw3

                   movb    #led2on, portb          ; LED2 will light if Port H bit 3 low

               ldd    #sec            

               jsr    DELAY             ; delay time = (Reg D) * msec

   sw3:       brset    porth, #sw3on, loop     ; if bit 2 Port H high, branch to loop

               movb    #led3on, portb          ; LED3 will light if Port H bit 2 low

               ldd    #five_sec         

               jsr    DELAY             ; delay time = (Reg D) * msec

               bra    loop

               swi                ; end the program

DELAY:

               pshd

               pshx

               pshy

            

               tfr        D,Y    ; (D) -> (Y)

   starty: ldx        #msec    ; start y loop and set x loop to 1 msec

   startx: dex            ; start x loop - 4 cycles per startx loop if branch

               bne        startx    

               dey        

               bne        starty

            

               puly

               pulx

               puld

            

               rts

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