ON 20050328@7:03:38 PM at page:
http://piclist.com/techref/microchip/delay/xb1crnm-ng.htm#38439.7941898148
Nikolai Golovchenko [NG--944] Code:

<PRE>The PIC delay routine above works correctly only if d3 and d4 are zero (the same is probably true for the SX version as well). The problem lies in how the routine is extended by adding another loop. Basically, every time a loop is appended, it adds at least 2 cycles, which must be subtracted. Sometimes, it can be done by moving the jump target by 2 nops down, but when there are no more nops, it can be done by subtracting one from d1, which subtracts 4 cycles. So d1 is decremented, a new loop adds 3 cycles and subtracts 4, which is -1 overall. So the jump should include an additional nop. 

The corrected PIC version is below:

; preincrement counters except d0
                                incf    d1, f
                                incf    d2, f
                                incf    d3, f
                                incf    d4, f

; Let Delay = 0 at this point
                                comf    d0, w
                                andlw   0x03
                                addwf   PCL, f

                                nop
Delay2                          nop
Delay1                          nop

; Delay = 4 + d0

Delay0                          decfsz  d1, f
                                 goto   Delay1
                                 
; Delay = 6 + d0 + 4 * d1

                                decf    d1, f
                                decfsz  d2, f
                                 goto   Delay2

; Delay = 9 + d0 + 4 * (d1 + 256 * d2)


                                decfsz  d3, f
                                 goto   Delay0

; Delay = 11 + d0 + 4 * (d1 + 256 * d2 + 256^2 * d3)

                                decf    d1, f
                                decfsz  d4, f
                                 goto    Delay1

; Delay = 14 + d0 + 4 * (d1 + 256 * d2 + 256^2 * d3 + 256^3 * d4)


; This can be extended like this:
;
;   decf d1, f
;   decfsz d5, f
;    goto Delay2
;
;   decfsz d6, f
;    goto Delay0
;
;   decf d1, f
;   decfsz d7, f
;    goto Delay1
;
;   decf d1, f
;   decfsz d8, f
;    goto Delay2
;
;   decfsz d9, f
;    goto Delay0
</PRE>