;#############################################################################
;#              VAULT INFORMATION SERVICES - 8052 CODE EXAMPLE               #
;#             (C) Copyright 1997 by Vault Information Services              #
;#                                                                           #
;# This code fragment is provided to the public free of charge and WITHOUT   #
;# OF ANY KIND,  NEITHER EXPRESS OR IMPLIED.   This code is offered as  an   #
;# example of  8052  programming.   VIS extends no warranty regarding  its   #
;# functionality or fitness for a specific purpose.;#                        #
;# The user may  utilize this code in  any way he/she sees fit,  including   #
;# using it in his/her own program,  commercial or otherwise.  However, by   #
;# using this  code the  user states his/her  acceptance of the  above and   #
;# holds  VIS indemnified against any and all claims that may arise due to   #
;# the use or misuse of this code.                                           #
;#---------------------------------------------------------------------------#
;# PURPOSE OF CODE FRAGMENT: The following code fragment includes a function #
;#  called "DEC_DPTR."  DEC_DPTR, when executed, will perform the exact      #
;#  opposite of the "INC DPTR" 8052 instruction--it will decrement the value #
;#  in DPTR by one.  No other registers or flags will be affected.           #
;#############################################################################

DEC_DPTR:
    XCH     A,DPL               ;Exchange A for DPL
    DEC     A                   ;Decrement A (which is DPL)
    CJNE    A,#0FFh,_dec_dptr2  ;If A (DPL) is not #0FFh, continue normally
    DEC     DPH                 ;If A=FFh, we need to decrement DPH
_dec_dptr2:
    XCH     A,DPL               ;Exchange A for DPL (thus saving DPL and restoring A)
    RET

    END