di2594l1.txt 
;**************************************************************************************************
; LISTING 1 - DEBUGGING SUBROUTINE
;
; "PIC debugging routine reads out binary numbers," EDN, Dec 7, 2000, pg 196

; http://www.ednmag.com/ednmag/reg/2000/12072000/designideas.htm#25di5
;
***************************************************************************************************

;Define the pin to be used as the test point:
#define  TP1        5,4         ;bit 4 of Port A.

;Allocate a register for use by the debug subroutine:
    cblock
    DebugReg
    endc

;---------------------------------------------------------------
; This subroutine takes the contents of the W register and shifts 
; it out, bit by bit, on the TP1 port pin for viewing on a scope.  
; Long pulse is a one and short pulse is a zero.  W register and 
; flags are preserved!
Debug
    movwf   DebugReg            ;Store value in reg.
    rlf     DebugReg            ;Shift MSB into CY.
    bcf     TP1                 ;"Start of byte" transition.
    btfsc   C                   ;If bit is set,
    bsf     TP1                 ;start pulse sooner,
    rlf     DebugReg
    bsf     TP1                 ;rather than later.
    bcf     TP1                 ;End of pulse.
    btfsc   C                   ;Test next bit and repeat...
    bsf     TP1
    rlf     DebugReg
    bsf     TP1
    bcf     TP1
    btfsc   C
    bsf     TP1
    rlf     DebugReg
    bsf     TP1
    bcf     TP1
    btfsc   C
    bsf     TP1
    rlf     DebugReg
    bsf     TP1
    bcf     TP1
    btfsc   C
    bsf     TP1
    rlf     DebugReg
    bsf     TP1
    bcf     TP1
    btfsc   C
    bsf     TP1
    rlf     DebugReg
    bsf     TP1
    bcf     TP1
    btfsc   C
    bsf     TP1
    rlf     DebugReg
    bsf     TP1
    bcf     TP1
    btfsc   C
    bsf     TP1
    rlf     DebugReg            ;Restore CY flag.
    bsf     TP1
    bcf     TP1
    nop                         ;Optional to provide consistent timing.
    bsf     TP1                 ;"End of byte" transition.
    return