SEI

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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[edit | edit source]

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[edit | edit source]

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