Sbc Subtract With Carry - Samsung S3C8275X User Manual

S3C8275X/F8275X/C8278X/F8278X/C8274X/F8274X
SBC
— Subtract with Carry
SBC dst,src
dst ← dst – src – c
Operation:
The source operand, along with the current value of the carry flag, is subtracted from the
destination operand and the result is stored in the destination. The contents of the source are
unaffected. 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 the low-order operands to be subtracted from the subtraction of
high-order operands.
C: Set if a borrow occurred (src > dst); cleared otherwise.
Flags:
Z: Set if the result is "0"; cleared otherwise.
S: Set if the result is negative; cleared otherwise.
V: Set if arithmetic overflow occurred, that is, if the operands were of opposite sign and the sign
of the result is the same as the sign of the source; cleared otherwise.
D: Always set to "1".
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".
Format:
opc
opc
opc
Examples: Given: R1 = 10H, R2 = 03H, C = "1", register 01H = 20H, register 02H = 03H,
and register 03H = 0AH:
SBC
SBC
SBC
SBC
0AH
SBC
In the first example, if working register R1 contains the value 10H and register R2 the value 03H,
the statement "SBC R1,R2" subtracts the source value (03H) and the C flag value ("1") from the
destination (10H) and then stores the result (0CH) in register R1.
dst | src
src dst
dst src
→
R1,R2 R1 = 0CH, R2 = 03H
→
R1,@R2 R1 = 05H, R2 = 03H, register 03H = 0AH
→
01H,02H Register 01H = 1CH, register 02H = 03H
01H,@02H →
Register 01H = 15H,register 02H = 03H, register 03H =
→
01H,#8AH Register 01H = 95H; C, S, and V = "1"
Bytes Cycles Opcode
2 4
6
3 6
6
3 6
INSTRUCTION SET
Addr Mode
(Hex) dst src
32 r r
33 r lr
34 R R
35 R IR
36 R IM
6-77