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
Words
1 (2 bytes)
Cycles
1
Parent topic: SBC – Subtract with Carry