Chapter
3.
Instruction
Set
SBB
3-56
Opcode
Operand
RZ
Operands are not permitted with the
RZ
instruction.
o 0
Cycles:
States:
Addressing:
Flags:
Example:
o
O~
or 3
5 or
11
(6
or
12
on 8085)
register indirect
none
For the sake
of
brevity, an example
is
given for the RET instruction but
oot
for each
of
its closely related
variants.
SUBTRACT
WITH
BORROW
SBB
subtracts one byte
of
data and the setting
of
the carry flag from the contents
of
the accumulator. The
result
is
stored
in
the accumulator.
SBB
then updates the setting of the carry flag to indicate the outcome of
the operation.
SBB's use of the carry
flag enables the program to subtract Ilulti-byte strings.
SBB
incorporates the carry flag
by
adding it
to
the byte
to
be
subtracted from the accumulator. It then subtracts the result from the accumulator
by
using two's complement addition. These preliminary operations occur
in
the processor's internal work registel
so
that
the source data remains unchanged.
Subtract Register from
Accumulator
with Borrow
Opcode Operand
SBB
reg
The operand must specify one of the registers A through
E,
H or
L.
This instruction subtracts the contents of
the specified register and the carry
flag from the accumulator and stores the result
in
the accumulator.
o 0
Cycles:
States:
Addressing:
Flags:
S
s3
4
register
Z,S,P,CY,AC
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