97. SBC – Subtract with Carry
97.1. Description
Subtracts two registers and subtracts with the C Flag, and places the result in the destination register Rd.
Operation:
(i) Rd ← Rd - Rr - C
Syntax: Operands: Program Counter:
(i) SBC Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
0000 10rd dddd rrrr
97.2. Status Register (SREG) and Boolean Formula
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔
H Rd3 • Rr3 + Rr3 • R3 + R3 • Rd3
Set if there was a borrow from bit 3; cleared otherwise.
S N ⊕ V, for signed tests.
V Rd7 • Rr7 • R7 + Rd7 • Rr7 • R7
Set if two’s complement overflow resulted from the operation; cleared otherwise.
N R7
Set if MSB of the result is set; cleared otherwise.
Z R7 • R6 • R5 • R4 • R3 • R2 • R1 • R0 • Z
Previous value remains unchanged when the result is zero; cleared otherwise.
C Rd7 • Rr7 + Rr7 • R7 + R7 • Rd7
Set if the absolute value of the contents of Rr plus previous carry is larger than the absolute value of
the Rd; cleared otherwise.
R (Result) equals Rd after the operation.
Example:
; Subtract r1:r0 from r3:r2
sub r2,r0 ; Subtract low byte
sbc r3,r1 ; Subtract with carry high byte
Atmel AVR Instruction Set Manual [OTHER]
Atmel-0856L-AVR-Instruction-Set-Manual_Other-11/2016
147
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