SEI
From C64-Wiki
Revision as of 22:11, 8 November 2007 by BinaryDane (Talk | contribs)
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 respond to IRQ, use the complementary instruction CLI.
[edit] 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.
[edit] CPU flags
SEI only affects the interrupt status flag, which is always unconditionally set.
