User's Manual

THE 80286 INSTRUCTION SET
SBB-Integer Subtraction With Borrow
Opcode
Instruction Clocks
18
Ir
SBB eb,rb
2,mem=7
19 jr SBB eW,rw
2,mem=7
1A
Ir
SBB rb,eb
2,mem=7
1B
Ir
SBB rW,ew
2,mem=7
1C db
SBB AL,db
3
10 dw SBB AX,dw
3
80
13
db
SBB eb,db 3,mem=7
81
13
dw SBB eW,dw 3,mem=7
83
13
db
SBB eW,db
3,mem=7
FLAGS MODIFIED
Overflow, sign, zero, auxiliary carry, parity, carry
FLAGS UNDEFINED
None
OPERATION
Description
Subtract with borrow byte register from EA
byte
Subtract with borrow word register from
EA
word
Subtract with borrow EA byte from byte
register
Subtract with borrow EA word from word
register
Subtract with borrow imm. byte from AL
Subtract with borrow imm. word from AX
Subtract with borrow imm. byte from EA byte
Subtract with borrow imm. word from EA word
Subtract with borrow imm. byte from EA word
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