RTI

Basic Info
Addressing Mode	Opcode	Length	Speed
Stack (RTI)	40	1 byte	7 cycles*

Flags Affected
	N	V	M	X	D	I	Z	C
65c816 native mode
6502 emulation mode			.	.

RTI (ReTurn from Interrupt) is a 65x instruction used to return control from an interrupt handler. It does this by first pulling the flags off of the stack and then the program counter too.

Syntax

RTI

Pitfalls

• RTI should only be run when the e flag is in the same state as when the interrupt fired
• RTI cannot even tell whether the interrupt actually occurred or not
• RTI does not increment the program counter after pulling it like RTS and RTL do

Cycle Skipped

RTI takes one fewer cycle in emulation mode as the program bank register doesn't need to be pulled from the stack.

See Also

• BRK
• RTS
• RTL
• RETI
• PLP

External Links

• Eyes & Lichty page 492, on RTI: https://archive.org/details/0893037893ProgrammingThe65816/page/492
• Labiak page 176 on RTI: https://archive.org/details/Programming_the_65816/page/n186
• MCS6500 Manual page 132 on RTI: https://archive.org/details/mos_microcomputers_programming_manual/page/n152
• Carr page 270 on RTI: https://archive.org/details/6502UsersManual/page/n283
• Leventhal page 3-89 on RTI: https://archive.org/details/6502-assembly-language-programming/page/n138
• snes9x implementation of RTI: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3272
• undisbeliever on RTI: https://undisbeliever.net/snesdev/65816-opcodes.html#rti-return-from-interrupt
• Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#RTI
• Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.3.2