SEI

SEI (short for "SEt Interrupt flag") is the mnemonic for a machine language instruction which sets the interrupt flag, thereby preventing the CPU from responding to IRQ interrupt events. To re-enable the response to IRQs, use the complementary instruction CLI.

Addressing mode

Opcode		Addressing mode	Assembler format	Length in bytes	Number of cycles
Dec	Hex
120	78	Implied	SEI	1	2

SEI only supports the Implied addressing mode, as shown in the table at right.

CPU flags

SEI only affects the interrupt status flag, which is always unconditionally set.