BRK: Difference between revisions

Revision as of 04:39, 11 August 2024


Basic Info
Addressing Mode	Opcode	Length	Speed
Stack (Interrupt)	00	2 bytes	8 cycles*


Flags Affected
	N	V	M	X / B	D	I	Z	C
65c816 native mode	.	.	.	.	0	1	.	.
6502 emulation mode	.	.	.	1	0	1	.	.

BRK (Break) is a 65x instruction designed to trigger a software interrupt. The byte following the opcode is called the signature byte. The state of the interrupt disable flag has no effect on the behavior of BRK although it will be set after BRK runs. In other words, BRK causes an NMI.

Control is routed to the BRK handler, whose address is stored at the BRK vector:

In native mode, this vector is at $00:FFE6.
In emulation mode, this vector is at $FFFE.

The PBR is cleared, but in native mode its previous value is pushed to the stack.

Syntax

BRK
BRK sig

Cycle Skipped

BRK takes one fewer cycle in emulation mode as it doesn't need to push the program counter bank register to the stack.

External Links

Eyes & Lichty, page 436 on BRK
Figure 13.3. illustration. Lbid. page 256
Labiak, page 126 on BRK
9.11 on MCS6500 Manual, page 144 on BRK
Carr, page 252 on BRK
Leventhal, page 3-49 on BRK
snes9x implementation of BRK: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L2547
Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#BRK
https://undisbeliever.net/snesdev/65816-opcodes.html#software-interrupts

@@ Line 63: / Line 63: @@
 ===== Cycle Skipped =====
 BRK takes one fewer cycle in [[emulation mode]] as it doesn't need to push the [[program counter bank register]] to the [[stack]].
+[[File:brk.png]]
 === See Also ===