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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.
Note that the signature for BRK may be any value, whereas the signature for COP should be limited to the range $00-$7F. [ 2 ] The use of BRK and/or COP to request an operating system service means user applications do not have to know the entry address of each operating system function, only the correct signature byte to invoke the desired ...
Boards. Grant's 7/8-chip 6502 board Archived 2022-06-06 at the Wayback Machine; 6502 microprocessor training board Archived 2019-07-14 at the Wayback Machine; Build your own KIM-1 training board Archived 2019-07-14 at the Wayback Machine – see KIM-1; 6502 home computer on GitHub; PE6502 single board computer Archived 2020-05-03 at the Wayback ...
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 ...
The Motorola 6800 microprocessor was the first for which an undocumented assembly mnemonic HCF became widely known. The operation codes (opcodes—the portions of the machine language instructions that specify an operation to be performed) hexadecimal 9D and DD were reported and given the unofficial mnemonic HCF in a December 1977 article by Gerry Wheeler in BYTE magazine on undocumented ...
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 ...
The FPO2 escape opcodes are used by the NEC 72291 floating-point coprocessor - this coprocessor also uses the standard D8-DF escape opcodes, but uses them to encode an instruction set that is unique to the 72291 and not compatible with x87. A listing of the opcodes/instructions supported by the 72291 is available. [34] BRKEM imm8: 0F FF ib
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.