8051 Program - subtract acc from dptr

; Description:

; Subtract Acc From DPTR, Setting Carry If DPTR Underflows

;

; Entry Requirements:

; DPTR Has Value

; Acc Has Value To Subtract

;

; On Exit:

; DPTR = DPTR - Acc, CY Set Accordingly

;

; Affected:

; PSW.CY, DPTR

;

; Stack:

; 1 Bytes, Not Including Space Used By Called Routines

;

; Comments:

; Value Of CY On Entry Does Not Affect Result

;

UTIL_SUBBAD:
	push acc	; Make Sure Acc Gets Saved
	clr c	; Clear For SUBB
	xch a,dpl	; Swap
	subb a,dpl	; Subtract
	mov dpl,a	; Move Back To DPL
	mov a,dph	; Get DPH
	subb a,#000h	; If Carry Set, This Will Decrement
	mov dph,a	; Move Back To DPH
	pop acc	; Recover Original 'A'
	ret	; Return To Caller

Source: Assorted Utilities, John C. Wren 11/23/96

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List of topics: 8051

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