PIC184550: Program seems to terminate at call function

Question

I'm writing a program that will blink red, yellow, and green LEDs off and on to match the function of a traffic light. However, when I run it in the debugger and step through (I am using MPLAB X IDE), it seems to stop after calling the function 'LOOP1'. The value reflected in PORTD is the value it should hold after completion of LOOP1, rather than after completion of LOOP6. Any ideas?

 list p=18f4550, r=DEC
 #include <p18f4550.inc>
 CONFIG LVP=OFF
 CONFIG WDT=OFF
 CONFIG MCLRE=OFF

 CONFIG FOSC = INTOSCIO_EC

    ORG 0x00
    CBLOCK 0
DELAY1:1
DELAY2:1
COUNTER:1
    ENDC

START:
    CLRF TRISD
    CLRF PORTD
    CLRF COUNTER
    CLRF DELAY1
    CLRF DELAY2
    MOVLW 0x00

PRIMARYLOOP:
    CALL LOOP1
    CALL LOOP2
    CALL LOOP3
    CALL LOOP4
    CALL LOOP5
    CALL LOOP6
    GOTO PRIMARYLOOP

LOOP1:
    MOVLW b'00010010'
    MOVWF PORTD
    MOVLW 0x01
    MOVWF COUNTER
    CALL DELAYMAIN
    RETURN
LOOP2:
    MOVLW b'01000010'
    MOVWF PORTD
    MOVLW 0x05
    MOVWF COUNTER
    CALL DELAYMAIN
    RETURN
LOOP3:
    MOVLW b'00100010'
    MOVWF PORTD
    MOVLW 0x03
    MOVWF COUNTER
    CALL DELAYMAIN
    RETURN
LOOP4:
    MOVLW b'00010010'
    MOVWF PORTD
    MOVLW 0x01
    MOVWF COUNTER
    CALL DELAYMAIN
    RETURN
LOOP5:
    MOVLW b'01000010'
    MOVWF PORTD
    MOVLW 0x05
    MOVWF COUNTER
    CALL DELAYMAIN
    RETURN
LOOP6:
    MOVLW b'00100010'
    MOVWF PORTD
    MOVLW 0x03
    MOVWF COUNTER
    CALL DELAYMAIN
    RETURN

DELAYMAIN:
    DECFSZ DELAY1,1
    GOTO DELAYMAIN
    DECFSZ DELAY2,1
    GOTO DELAYMAIN
    DECFSZ COUNTER,0,0
    RETURN

    END

score 0 · Answer 1 · answered Apr 10 '15 at 00:47

You're skipping the return instruction in DELAYMAIN, causing execution to go beyond the program. The rest of memory likely contains NOP instructions, so control will continue until the PC wraps around to 0 and the program restarts.

Simply add the missing GOTO (or BRA) instruction after the last DECFSZ and it should get to the second loop. You also need to change the destination of that DECFSZ to write to the register, or it will never finish when COUNTER > 1.

PIC184550: Program seems to terminate at call function

1 Answers1