This content has not been validated; it was AI-generated following the x86-64 ISA Documentation generation process to maintain high quality. However, as no human has verified this data, errors may exist. If the accuracy of this data is critical, please consult the Intel SDM. The model used to generate this is gemma4:31b

OUTSB

Outputs the byte at the address pointed to by rSI to the I/O port specified by rDX, then increments or decrements rSI by 1 based on the Direction Flag (DF).

The following table covers the supported source and destination operands.

DO NOT support LOCK

This instruction is available in 64-bit mode, compatibility mode, and 32-bit protected mode. In 64-bit mode, the rSI and rDX registers are used as 32-bit registers.

The instruction relies on the Direction Flag (DF) in the RFLAGS register; if DF=0, rSI is incremented; if DF=1, rSI is decremented. When used with the REP prefix, the instruction repeats until rCX is 0. If rCX is 0 initially, the instruction does not execute. Ensure that the memory region pointed to by rSI is accessible to avoid a general-protection exception (#GP).