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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 ...
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.
MOS Technology 65xx (e.g. 6502) NOP: 1 0xEA NOP consumes two clock cycles. Undefined opcodes in the NMOS versions of the 65xx family were converted to be NOPs of varying instruction lengths and cycle times in the 65C02. PA-RISC: NOP: 4 0x08000240 Opcode for OR 0,0,0. [7] LDI 26,0: 4 0x34000034
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 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 ...
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.
A directive issued by Marine Corps headquarters on Tuesday "asked the fleet to PAUSE on all [Sexual Assault Prevention and Reporting] training due to recent changes within the White House to ...
6502 - the first RISC µP – With link to concise 6502 programming chart in PDF (Eric Clever).[] On 12 November 2006 this was "reworded" and moved to the 6502 trivia section. A magazine article once referred to the 6502 as the original RISC processor, due to its efficient and simple instruction set and its 256 zero-page "registers."