Apple II manual Acc, Subtract, POP DOUBLE-BYTE Indirect

EXAMPLE:
14	34	A0	SET	R4	$A034	;Init pointers
15	22	90	SET	R5	$9022
84			POP	@R4		;Move byte from
95			STP	@R5		;$A033 to $9021
84			POP	@R4		;Move byte from
95			STP	@R5		;$A032 to $9020
ADD:
ADD Rn					[ An ]

The contents of Rn are added to the contents of ACC (R0), and the low-order 16 bits of the sum restored in ACC. the 17th sum bit becomes the carry and the other branch conditions reflect the final ACC contents.

EXAMPLE:

10	34	76	SET	R0	$7634	;Init R0 (ACC) and			R1
11	27	42	SET	R1	$4227
A1			ADD	R1		;Add R1	(sum=B85B,		C clear)
A0			ADD	R0		;Double	ACC	(R0) to $70B6
						;with carry		set.

SUBTRACT:

SUB Rn [ Bn ]

The contents of Rn are subtracted from the ACC contents by performing a two's complement addition:

ACC = ACC + Rn + 1

The low order 16 bits of the subtraction are restored in the ACC, the 17th sum bit becomes the carry and other branch conditions reflect the final ACC contents. 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. Rn is not disturbed.

EXAMPLE:

10	34	76	SET	R0	$7634	;Init R0 (ACC)
11	27	42	SET	R1	$4227	;and R1
B1			SUB	R1		;subtract R1
						;(diff=$340D	with c set)
B0			SUB	R0		;clears ACC. (R0)

POP DOUBLE-BYTE INDIRECT:

POPD @Rn [ Cn ]

Rn is decremented by 1 and the high-order ACC byte is loaded