Apple II manual Compare, BF A0 SET $A0BF, LOOP1 SUB, BNC LOOP1, Increment

from the memory location whose address now resides in Rn. Rn is again decremented by 1 and the low-order ACC byte is loaded from the corresponding memory location. Branch conditions reflect the final ACC contents. The carry is cleared. Because Rn is decremented prior to loading each of the ACC halves, double-byte stacks may be implemented with the STD @Rn and POPD @Rn ops

(Rn is the stack pointer).

EXAMPLE:

15	34	A0	SET	R5	$A034	;Init stack pointer
10	12	AA	SET	R0	$AA12	;Load $AA12 into ACC
75			STD	@R5		;Push $AA12 onto stack
10	34	BB	SET	R0	$BB34	;Load $BB34 into ACC
75			STD	@R5		;Push $BB34 onto stack
C5			POPD	@R5		;Pop $BB34 off stack
C5			POPD	@R5		;Pop $AA12 off stack

COMPARE:

CPR Rn [ Dn ]

The ACC (R0) contents are compared to Rn by performing the 16 bit binary subtraction ACC-Rn and storing the low order 16 difference bits in R13 for subsequent branch tests. If the 16 bit unsigned ACC contents are greater than or equal to the 16 bit unsigned Rn contents, then the carry is set, otherwise it is cleared. No other registers, including ACC and Rn, are disturbed.

EXAMPLE:

15	34	A0		SET	R5	$A034	;Pointer to memory
16	BF A0			SET	R6	$A0BF	;Limit address
B0			LOOP1	SUB	R0		;Zero data
75				STD	@R5		;clear 2 locations
							;increment R5 by 2
25				LD	R5		;Compare pointer R5
D6				CPR	R6		;to limit R6
02	FA			BNC	LOOP1		;loop if C clear

INCREMENT:

INR Rn [ En ]

The contents of Rn are incremented by 1. The carry is cleared and other branch conditions reflect the incremented value.

EXAMPLE:

15	34 A0	SET	R5	$A034	;(Pointer)
B0		SUB	R0		;Zero to R0
55		ST	@R5		;Clr Location $A034
E5		INR	R5		;Incr R5 to $A036
55		ST	@R5		;Clrs location $A036
					;(not $A035)