Operations:

Syntax:

Operation:

Operands:

Program Counter:

Opcode

Comment

Stack

SBC Rd,Rr

Rd = Rd - Rr - C

0 <= d <= 31, 0 <= r <= 31

PC = PC + 1

000010rdddddrrrr

Description

Subtracts two registers and subtracts with the C flag, and places the result in the destination register Rd.

Status Register (SREG) and Boolean Formula

I

–

T

–

H

⇔

~Rd3 AND Rr3 OR Rr3 AND R3 OR R3 AND ~Rd3

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

S

⇔

N XOR V, for signed tests.

V

⇔

Rd7 AND ~Rr7 AND ~R7 OR ~Rd7 AND Rr7 AND 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 AND ~R6 AND ~R5 AND ~R4 AND ~R3 AND ~R2 AND ~R1 AND ~R0 AND Z

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

C

⇔

~Rd7 AND Rr7 OR Rr7 AND R7 OR R7 AND ~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)

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)

Table Cycles

Name

Cycles

AVRe

1

AVRxm

1

AVRxt

1

AVRrc

1