Parameters are often passed fixed memory locations

Programming the 65816

0001		L123	KEEP	KL.12.3
0002
0003			START
0004	0 0 0 0		START
0005
0006
0007	0 0 0 2
0007	0 0 0 2		SEP	# $ 2 0
0008			SEP	# $ 2 0
0009		STRING1
0010	0004
0010	0004		REP	# $ 1 0
			REP	# $ 1 0
0012
0013	0006				pass the address of STRING1 to PRSTRNG
0013	0006		LDX	#STRING1
0014	0006 A21500		LDX	#STRING1
0015			JSR
0016			JSR
0016			LDX	#STRING2	pass the address of STRING2 to PRSTRNG
0017	OOOC A22800		LDX	#STRING2	pass the address of STRING2 to PRSTRNG
0018	0 0 0 F 200080		JSR
0019			JSR
0019
0020	0012 38
0021	0013 FB
0021	0013 FB
0022
0023	0015
0023	0015		DC
0024	0015 54686973		DC
0025	0028 54686973	STRING2
0026	003 B	STRING2

0027		12
0027
0028		; print a string of characters terminated by a 0 byte
0029	0 0 0 0	; print a string of characters terminated by a 0 byte
0030
0030		PRSTRNG	START
0031
0032	0 0 0 0
0033		TOP	LDA		get char at index position in string
0034		BEQ			if character is 0 , return
0035	0005 200080	JSR
0036		INX
0037	0009 80F5	BRA		TOP
0038		DONE
0039		END
0040	oooc	END
0041		1
0042
0043
		1	machine-dependent routine to output a character
	0 0 0 0	1	machine-dependent routine to output a character
0044	0 0 0 0
0045
0045		COUT
0046		ECOUT	GEQU	$FDED	Apple // COUT
0047		PHA
0048		PHA
0048
0049	0002 5A	PHY
0050		PHP
0051		SEC
0052	0005 FB	XCE
0053		JSR
0054		CLC.
0055	000A FB	XCE
0056		PLP
0057		PLY			restore registers
0058	000D FA	PLY			restore registers
0058	000D FA	PLX
0059
0060		RTS
0061	0 0 1 0