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SBB
Encoding:
SUBTRACT WITH
BORROW
SBB
Memory or Register Operand and Register Operand:
I
0001
1 0 d w I mod reg r / m I
if d = 1 then LSRC = REG, RSRC = EA, OEST = REG
else LSRC = EA, RSRC = REG, OEST = EA
Immediate Operand from Memory or Register Operand:
11
00000
s w I modO 1 1 r / m I
data
Idata if
s:w=011
LSRC = EA, RSRC = data, OEST = EA
Immediate Operand from Accumulator:
I
00011
1 0 w I data I data
if
w=1
I
if w = 0 then LSRC = AL, RSRC = data, OEST =
AL
else LSRC = AX, RSRC = data, OEST = AX
SBB Operands
Clocks·
Transfers
Bytes
register, register 3
-
2
register, memory 9(13) + EA 1
2-4
memory, register 16(24) + EA 2
2-4
accumulator, immediate 4
-
2-3
register, immediate
4
-
3-4
memory, immediate 17(25) + EA 2
3-6
SBB Coding Example
SBB
BX, CX
SBB
01,
[BX].PAYMENT
SBB
BALANCE,
AX
SBB
AX, 2
SBB
CL,
1
SBB
COU
NT
[SI],
10
*b(w): where b denotes the number of clock cycles
for
byte operands and
w
denotes
the
number
of clock cycles for word operands.
2-148