hw19SLN - ECE 212 HW Set 19 SOLUTIONS p 1 of 10

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ECE 212 HW Set 19 SOLUTIONS p 1 of 10 //home/vdimitrov/9117/53b8521898f646d1f885b4166fe826fd51d9a63e.doc ECE 212 Homework Set 19 – SOLUTIONS 1. (a) For the green and red LEDs interfaced to Port B in lecture, write the subroutine GonRoff specified. (b) Complete the Destroys line of the documentation. ;Name: GonRoff ;Preconditions: None. ;Postcondition: None. ;Destroys: ;Description: Turn the four green LEDs on, the four ; red LEDs off. ; (The green LEDs are connected to bits ; 3, 2, 1, 0 of Port B; the red LEDS are ; connected to bits 7, 6, 5, 4.) GonRoff: NOTE: To turn an LED on, you must sent the value 1 to the corresponding bit. A Solution: ;Name: GonRoff ;Preconditions: None. ;Postcondition: None. ;Destroys: A, flags. ;Description: Turn the four green LEDs on, the four ; red LEDs off. GonRoff: movb #0b00001111,PortB ;Activate all LEDs at the same time. rts Another Solution: ;Name: GonRoff ;Preconditions: None. ;Postcondition: None. ;Destroys: Flags. ;Description: Turn the four green LEDs on, the four ; red LEDs off. GonRoff: bclr PortB,0b11110000 ;First turn off the red, bset PortB,0b00001111 ; Then turn on the green. rts
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ECE 212 HW Set 19 SOLUTIONS p 2 of 10 2. (a) For the eight switches interfaced to Port E in lecture, write the subroutine SW631OnOffOff specified. Use one 'compare' instruction in your routine, but do not use either brclr or brset . (b) Complete the Destroys line of the documentation. ;Name: SW631OnOffOff ;Preconditions: None. ;Postcondition: None. ;Destroys: ;Description: if (SW6 is On ; AND ; SW3 is Off ; AND ; SW1 is Off) A = 1; ; else A = 0; SW631OnOffOff: NOTE: An 'on' switch produces a 0 at the port. Therefore the 'if' condition is that Port E has the value x0xx1x1x, where 'x' denotes a don't-care. One Solution: ;Name: SW631OnOffOff ;Preconditions: None. ;Postcondition: None. ;Destroys: (A), B, flags. ;Description: if (SW6 is On ; AND ; SW3 is Off ; AND ; SW1 is Off) A = 1; ; else A = 0; SW631OnOffOff: ldaa #1 ;Anticipate success. ldab PortE ;Get the switch status, andb #0b01001010 ; isolate bits 6,3,1. cmpb #0b0 0 00 1 0 1 0 ;Looking for 0 1 1 beq OnOffOff ;Got it. deca ;Nope -- make A = 0. OnOffOff: rts
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ECE 212 HW Set 19 SOLUTIONS p 3 of 10 3. Write the subroutine NumberOfSWsOn specified below. The subroutine refers to the eight switches interfaced to Port E in lecture. ;Name:
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hw19SLN - ECE 212 HW Set 19 SOLUTIONS p 1 of 10

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