list p=16f627
    include "p16f627.inc"
    errorlevel -302

    __CONFIG 0x3D18

    movlw 0x07
    movwf CMCON

    banksel TRISA

    movlw 0xFF
    movwf TRISA
    clrf TRISB

    banksel PORTA

t1  equ 0x20
t2  equ 0x21
t3  equ 0x22
tn  equ 0x23

main:
    clrf    PORTB

loop:
    bsf PORTB, 0        ; Set green light

    btfss   PORTA, 0        ; Check if switch is pressed
    goto    loop            ; Switch isn't pressed so stay green

    movlw   3           ;
    movwf   tn          ; Delay 3 seconds
    call    delay_n         ;

    bcf PORTB, 0        ; Clear green light

    movlw   3           ;
    movwf   tn          ; Set up for 3 second delay

    bsf PORTB, 1        ; Set amber light
    call    delay_one       ; Delay one second

    bcf PORTB, 1        ; Clear amber light
    call    delay_one       ; Delay one second

    decfsz  tn, f           ; Decrement tn
    goto    $-5         ; Go back and repeat if tn isn't 0

    bsf PORTB, 2        ; Set red light

    movlw   5           ;
    movwf   tn          ; Delay 5 seconds
    call    delay_n         ;
    bcf PORTB, 3        ; Clear red light

    goto    loop

; Move n into tn before calling!
delay_n:
    decfsz  tn, f           ; Decrement until tn is zero
    goto    $+2         ; If it's not zero, jump ahead to delay by a second

    return              ; Otherwise the job is done

    call delay_one          ; Delay for a second
    goto delay_n            ; And return until it doesn't need to delay any more seconds

delay_one:
    movlw   0x8A            ;
    movwf   t1          ;
    movlw   0xBA            ;
    movwf   t2          ; I'll admit I cheated to find the best values for these
    movlw   0x03            ;
    movwf   t3          ;

delay_one_cycle:
    decfsz  t1, f           ; 1 cycle except if zero
    goto    $+2         ; 4 cycles
    decfsz  t2, f
    goto    $+2
    decfsz  t3, f
    goto    delay_one_cycle

    nop             ; 1 cycle

    return              ; 4 cycles including call

    end