Description:

Subtracts a constant from a register and subtracts with the C flag and places the result in the destination register Rd.

Operation:

(i)Rd ← Rd - K - C

Syntax: Operands: Program Counter:

(i) SBCI Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1

16-bit Opcode:

0100

KKKK

dddd

KKKK

Status Register and Boolean Formula:

I

T

H

S

V

N

Z

C

-

-

Set if there was a borrow from bit 3; cleared otherwise

S: N ⊕ V, For signed tests.

V:

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:

Z

Previous value remains unchanged when the result is zero; cleared otherwise.

C:

Set if the absolute value of the constant plus previous carry is larger than the absolute value of Rd; cleared otherwise.

R (Result) equals Rd after the operation.

Example:

; Subtract $4F23 from r17:r16
subi r16,$23 ; Subtract low byte
sbci r17,$4F ; Subtract with carry high byte

Words: 1 (2 bytes)

Cycles: 1