Question

8. The following program sequence tries to drive the LEDS so that LEDS-LEDO, LED2, LED4, LED6 turns on one at a time starting with LEDO and repeat. Each LED must be lighted for about half a second. But there are some errors in the program that are preventing the program to run successfully. Debug the program and rewrite it to make the program run successfully to perform the desired task [10 points HCS12 org $2000 movb $00,DDRB Idx movb 2,X+,portb jsr 1.5 KO PB7 DZww forever: led_tab PB6 ledIp: PBS delay 100ms epx Wled tab+10 bne led_Ip bra forever de.b S01,S00,$11,520 PB PB3 PB led_tab: PB ;Delay subroutine here end PBO

using assembly language

Answer 1

Answer :- First of all, the delay subroutine must be written. Next the instruction movb must use increment factor as 1 in place of 2 since data is of byte size. So the instruction would be -

movb 1, X+, portb

Same applies to the CPX instruction and it must be-

cpx #led_tab +5

Also the array data in led_tab is not correct and must be defined as-

led tab dc.b $01, $04, $10, $40

as $01 = 0000_0001, $04 = 0000_0100 and so on.

These four errors are preventing the code to give proper output.

Dear student, to write the delay subroutine we must know the frequency of the processor. Please comment on this.