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An illegal opcode, also called an unimplemented operation, [1] unintended opcode [2] or undocumented instruction, is an instruction to a CPU that is not mentioned in any official documentation released by the CPU's designer or manufacturer, which nevertheless has an effect.
The 65C802 could be retrofitted to a 6502 board and would function as a 65C02 on power-up, operating in "emulation mode." As with the 65C816, a two-instruction sequence would switch the 65C802 to "native mode" operation, exposing its 16-bit accumulator and index registers , and other 65C816 features.
The original 6502 has 56 instructions, which, when combined with different addressing modes, produce a total of 151 opcodes of the possible 256 8-bit opcode patterns. The remaining 105 unused opcodes are undefined, with the set of codes with low-order 4-bits with 3, 7, B or F left entirely unused, the code with low-order 2 having only a single ...
Internals of BRK/IRQ/NMI/RESET on a MOS 6502; Brad Taylor. "6502 'B' flag & BRK Opcode". 6502 Family Microprocessor Resources and Forum; 65xx Interrupt Primer – An extensive discussion of 65xx family interrupt processing. Investigating 65C816 Interrupts – An extensive discussion of interrupt processing that is specific to 65C816 native mode ...
Opcode for OR 0,0,0. [7] LDI 26,0: 4 0x34000034 Palindromic NOP - that is, an instruction that executes as NOP regardless of whether byte order is interpreted as little-endian or big-endian. Some PA-RISC system instructions are required to be followed by seven palindromic NOPs. [7] POWER, PowerPC, Power ISA: NOP: 4 0x60000000 Opcode for ori r0 ...
Ralf Brown's Interrupt List (aka RBIL, x86 Interrupt List, MS-DOS Interrupt List or INTER) is a comprehensive list of interrupts, calls, hooks, interfaces, data structures, CMOS settings, memory and port addresses, as well as processor opcodes for x86 machines from the 1981 IBM PC up to 2000 (including many clones), [1] [2] [nb 1] most of it still applying to IBM PC compatibles today.
This page was last edited on 14 July 2004, at 04:29 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may ...
3 6501<>6502 slot converters? 6 comments. 4 Clock multiplication. 1 comment. 5 Terminator 6502 code. 2 comments. 6 MOS Technology? 7 Memory Access. 18 comments. 8 MHz.