A.5.301 STC, STD, STI: Set Flags
STC ; F9 [8086]
STD ; FD [8086]
STI ; FB [8086]
These instructions set various flags. STC sets the carry flag; STD sets
the direction flag; and STI sets the interrupt flag (thus enabling
interrupts).
To clear the carry, direction, or interrupt flags, use the CLC, CLD and
CLI instructions (section A.5.20). To invert the carry flag, use CMC
(section A.5.22).