Intel 80286, 80287 manual SBB-Integer Subtraction With Borrow, Sbb

THE 80286 INSTRUCTION SET

SBB-Integer Subtraction With Borrow

Opcode			Instruction		Clocks	Description
18	Ir		SBB	eb,rb	2,mem=7	Subtract with borrow byte register from EA
						byte
19	jr		SBB eW,rw		2,mem=7	Subtract with borrow word register from EA
						word
1A	Ir		SBB rb,eb		2,mem=7	Subtract with borrow EA byte from byte
						register
1B	Ir		SBB rW,ew		2,mem=7	Subtract with borrow EA word from word
						register
1C	db		SBB AL,db		3	Subtract with borrow imm. byte from AL
10	dw		SBB	AX,dw	3	Subtract with borrow imm. word from AX
80	13	db	SBB	eb,db	3,mem=7	Subtract with borrow imm. byte from EA byte
81	13	dw	SBB	eW,dw	3,mem=7	Subtract with borrow imm. word from EA word
83	13	db	SBB eW,db		3,mem=7	Subtract with borrow imm. byte from EA word

FLAGS MODIFIED

Overflow, sign, zero, auxiliary carry, parity, carry

FLAGS UNDEFINED

None

OPERATION

The second operand is added to the carry flag and the result is subtracted from the first operand. The first operand is replaced with the result of the subtraction, and the flags are set accordingly.

When a byte-immediate value is subtracted from a word operand, the immediate value is first sign-extended.

PROTECTED MODE EXCEPTIONS

#GP(O) if the result is in a non-writable segment. #GP(O) for an illegal memory operand effective address in the CS, DS, or ES segments; #SS(O) for an illegal address in the SS segment.

REAL ADDRESS MODE EXCEPTIONS

Interrupt 13 for a word operand at offset OFFFFH.

B-99