stc

Set Carry Flag

STC

Sets the CF flag to 1.

Details

Unconditionally sets the Carry Flag (CF) to 1. Only the CF flag is modified; all other flags and CPU state remain unchanged. Available in all modes (real, protected, and 64-bit).

Pseudocode Operation

CF ← 1

Example

STC

Encoding

Binary Layout
F9
+0
 
Format Legacy
Opcode F9
Extension Base

Operands

Reference (Intel® SDM)

Instruction Forms

Opcode Instruction Op/En 64/32-bit Mode CPUID Description
F9 STC ZO Valid Valid Set CF flag.

Description

Sets the CF flag in the EFLAGS register. Operation is the same in all modes.

Operation

CF := 1;

Flags Affected

The CF flag is set. The OF, ZF, SF, AF, and PF flags are unaffected. Exceptions (All Operating Modes) #UD If the LOCK prefix is used. STC—Set Carry Flag Vol. 2B 4-671