mirror of
https://github.com/KarolS/millfork.git
synced 2024-07-31 09:29:05 +00:00
72 lines
1.5 KiB
Markdown
72 lines
1.5 KiB
Markdown
[< back to index](../index.md)
|
|
|
|
# Undocumented opcodes
|
|
|
|
## 6502
|
|
|
|
Original 6502 processors accidentally supported a bunch of extra undocumented instructions.
|
|
Millfork can emit them if so desired.
|
|
|
|
## Mnemonics
|
|
|
|
Since various assemblers use different mnemonics for undocumented opcodes,
|
|
Millfork supports multiple mnemonics per opcode. The default one is given first:
|
|
|
|
* **AHX**, AXA, SHA
|
|
|
|
* **ALR**
|
|
|
|
* **ANC**
|
|
|
|
* **ARR**
|
|
|
|
* **DCP**, DCM
|
|
|
|
* **ISC**, INS
|
|
|
|
* **LAS**
|
|
|
|
* **LAX**
|
|
|
|
* **LXA**, OAL
|
|
|
|
* **RLA**
|
|
|
|
* **RRA**
|
|
|
|
* **SAX**\*
|
|
|
|
* **SHX**, XAS
|
|
|
|
* **SHY**, SAY\*
|
|
|
|
* **SBX**, AXS\*\*
|
|
|
|
* **SRE**, LSE
|
|
|
|
* **SLO**, ASO
|
|
|
|
* **TAS**
|
|
|
|
* **XAA**, ANE
|
|
|
|
\* HuC2680 has different instructions also called SAX and SAY,
|
|
but Millfork can distinguish between them and the NMOS illegal instructions based on the addressing mode.
|
|
|
|
\*\* AXS is also used for SAX in some assemblers. Millfork interprets AXS based on the addressing mode.
|
|
|
|
## Generation
|
|
|
|
In order for the compiler to emit one of those opcodes,
|
|
an appropriate CPU architecture must be chosen (`nmos` or `ricoh`)
|
|
and either it must appear in an assembly block or it may be a result of optimization.
|
|
|
|
Optimization will never emit any of the following opcodes due to their instability and/or uselessness:
|
|
AHX, LAS, LXA, SHX, SHY, TAS, XAA.
|
|
|
|
## Z80
|
|
|
|
Original Z80 processors accidentally supported a bunch of extra undocumented instructions.
|
|
Millfork will not emit them.
|
|
The only exception is SLL, which will be emitted if it occurs in a handwritten assembly block.
|