; ********** SUBTRACT SEED SUBROUTINE **********
; SUBTRACTS FOUR BYTES OF SEED FROM (DE,HL).
;	ENTRY:	(SEED - SEED+3) = SEED #.
;			(DE,HL) = FOUR-BYTE VALUE.
;	EXIT:	(DE,HL) = RESULT OF SUBTRACT.
;			ALL REGISTERS SAVED EXCEPT DE, HL.
; **********************************************

.ORG	0000h
		
		LD	SP,	0080h		; ADDED FOR TESTING PURPOSES.
		LD	HL,	(SEED2 +2)	; ADDED FOR TESTING PURPOSES.
		LD	DE,	(SEED2)		; ADDED FOR TESTING PURPOSES.
		CALL SUB1			; ADDED FOR TESTING PURPOSES.
		HALT				; ADDED FOR TESTING PURPOSES.
		
SUB1:	PUSH	BC			; SAVE REGISTERS.
		LD	BC,	(SEED1 +2)	; GET LEAST SIGNIFICANT BYTE.
		OR	A				; RESET CARRY FLAG.
		SBC	HL,	BC			; SUBTRACT 2 LEAST SIGNIFICANT BYTES.
		EX	DE,	HL			; GET MOST SIGNIFICANT 2 BYTES.
		LD	BC,	(SEED1)		; GET MOST SIGNIFICANT 2 BYTES.
		SBC	HL,	BC			; SUBTRACT MS 2 BYTES AND CARRY.
		EX	DE,	HL			; NOW ORIGINAL - SEED.
		POP	BC				; RESTORE REGISTERS.
		RET					; RETURN.	

.ORG	0040h
SEED1:	.DB 22h,33h,44h,66h

.ORG	0050h
SEED2:	.DB	88h,0AAh,0CCh,0FFh

.END