UM012811-0904
eZ8 CPU Instruction Set Description
eZ8 CPU
User Manual
167
SBCX
Subtract with Carry using Extended Addressing
SBCX dst, src
Operation
dst
←
dst - src - C
Description
This instruction subtracts the source operand and the Carry (C) flag from the destination.
The destination stores the result. The contents of the source are unaffected. The eZ8 CPU
performs subtraction by adding the two’s-complement of the source operand to the desti-
nation operand. In multiple-precision arithmetic, this instruction permits the carry (bor-
row) from the subtraction of low-order operands to be subtracted from the subtraction of
high-order operands.
Flags
Attributes
Escaped Mode Addressing
Using Escaped Mode Addressing, address mode ER for the source or destination specifies
a Working Register with 4-bit addressing.
If the high byte of the source or destination address is
EEH
(11101110B), a Working Regis-
ter is inferred. For example, the operand
EE3H
selects Working Register R3. The full 12-
bit address is given by {RP[3:0], RP[7:4], 3H}.
To access Registers on Page EH (addresses
E00H
to
EFFH
), set the Page Pointer, RP[3:0],
to
EH
and set the Working Group Pointer, RP[7:4], to the desired Working Group.
C
Set if a borrow is required by bit 7; reset otherwise.
Z
Set if the result is zero; reset otherwise.
S
Set if the result is negative; reset otherwise.
V
Set if an arithmetic overflow occurs; reset otherwise.
D
Set to 1.
H
Set if a borrow is required by bit 3; reset otherwise.
Mnemonic Destination, Source
Opcode (Hex)
Operand 1
Operand 2
Operand 3
SBCX
ER1, ER2
38
ER2[11:4]
{ER2[3:0], ER1[11:8]} ER1[7:0]
SBCX
ER1, IM
39
IM
{0H, ER1[11:8]}
ER1[7:0]