We've just updated MediaWiki and its underlying software. If anything doesn't look or work quite right, please mention it to us. --RanAS
BRK: Difference between revisions
From SnesLab
(linkify) |
(bullet points) |
||
| Line 49: | Line 49: | ||
'''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. In other words, BRK causes an [[NMI]]. | '''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. In other words, BRK causes an [[NMI]]. | ||
Control is routed to the BRK handler, whose address is stored at the BRK vector | 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]]. | The [[PBR]] is cleared, but in [[native mode]] its previous value is pushed to the [[stack]]. | ||
Revision as of 02:45, 4 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. 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.
See Also
External Links
- Eyes & Lichty page 436, on BRK: https://archive.org/details/0893037893ProgrammingThe65816/page/436
- Figure 13.3. illustration. Lbid. page 256
- Labiak page 126 on BRK: https://archive.org/details/Programming_the_65816/page/n136
- MCS6500 Manual page 144 on BRK: https://archive.org/details/mos_microcomputers_programming_manual/page/n164
- Carr page 252 on BRK: https://archive.org/details/6502UsersManual/page/n265
- Leventhal page 3-49 on BRK: https://archive.org/details/6502-assembly-language-programming/page/n98
- 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