Z8
®
CPU
User Manual
UM001604-0108
Instruction Description
237
Subtract With Carry
Syntax
SBC dst, src
Instruction Format
Operation
dst
←
dst–src–C
The source operand, along with the setting of the C Flag, is subtracted from the destination
operand and the result is stored in the destination operand. The contents of the source
operand are not affected. Subtraction is performed by adding the two’s complement of the
source operand to the destination operand. In multiple precision arithmetic, this instruction
permits the carry (borrow) from the subtraction of low order operands to be subtracted
from the subtraction of high order operands.
Address modes R or IR can be used to specify a 4-bit Working Register. In this format, the
source or destination Working Register operand is specified by adding
1110b
(
Eh
) to the
high nibble of the operand. For example, if Working Register
R12 (CH)
is the destination
operand, then
ECh
is used as the destination operand in the Op Code.
Cycles
OPC
(Hex)
Address
Mode
dst
src
OPC
dst src
6
32
r
r
6
33
r
lr
OPC
src
dst
10
34
R
R
10
35
R
IR
OPC
dst
src
10
36
R
IM
10
37
IR
IM
Flag Description
C
Cleared if there is a carry from the most significant bit of the result; set otherwise,
indicating a
borrow
.
Z
Set if the result is 0; cleared otherwise.
V
Set if arithmetic overflow occurred (if the operands were of opposite sign and the
sign of the result is the same as the sign of the source); reset otherwise.
S
Set if the result is negative; cleared otherwise.
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
.
D
Always set to 1.
Note:
