Samsung S3C84E5 user manual SUB Subtract

INSTRUCTION SET S3C84E5/C84E9/P84E9

SUB — Subtract

SUBdst,src

Operation: dst ← dst – src

The source operand is subtracted from the destination operand and the result is stored in the destination. The contents of the source are unaffected. Subtraction is performed by adding the two's complement of the source operand to the destination operand.

Flags:	C: Set if a "borrow" occurred; cleared otherwise.
	Z: Set if the result is "0"; cleared otherwise.
	S: Set if the result is negative; cleared otherwise.
	V: Set if arithmetic overflow occurred, that is, if the operands were of opposite signs and the
	sign of the result is of the same as the sign of the source operand; cleared otherwise.
	D: Always set to "1".
	H: Cleared if there is a carry from the most significant bit of the low-order four bits of the

	result; set otherwise indicating a “borrow”.
Format:
				Bytes	Cycles	Opcode	Addr Mode
						(Hex)	dst	src
	opc	dst src		2	4	22	r	r
					6	23	r	lr
	opc	src	dst	3	6	24	R	R
					6	25	R	IR
	opc	dst	src	3	6	26	R	IM

Examples:	Given:	R1 = 12H, R2	= 03H, register 01H = 21H, register 02H = 03H, register 03H = 0AH:
	SUB	R1,R2	→	R1	= 0FH, R2 = 03H
	SUB	R1,@R2	→	R1	= 08H, R2 = 03H
	SUB	01H,02H	→	Register 01H		=	1EH, register 02H	=	03H
	SUB	01H,@02H	→	Register 01H		=	17H, register 02H	=	03H
	SUB	01H,#90H	→	Register 01H		=	91H; C, S, and V	=	"1"
	SUB	01H,#65H	→	Register 01H		=	0BCH; C and S =	"1", V = "0"

In the first example, if he working register R1 contains the value 12H and if the register R2 contains the value 03H, the statement "SUB R1,R2" subtracts the source value (03H) from the destination value (12H) and stores the result (0FH) in the destination register R1.

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