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The 6502 only has 56 opcodes. The db also includes modern variants of the 6502.
by gabrielsroka 3y ago
The 6502 only has 56 opcodes.
The db also includes modern variants of the 6502.
- dspillett 3y ago> The 6502 only has 56 opcodes In terms of bytes that the original CPU officially recognised as instructions, it was more like ~150 (working from old memories, I may be off by one or few there). Some of the other ~106 did something unofficially, and a number were valid instructions on later versions of the design. That ~150 were grouped into 56 instructions, many with multiple addressing modes (so "load A immediate", "load A direct", "load A indexed", etc, were different opcodes but considered the same instruction). Because register use was far from orthogonal (one accumulator, two index registers, and a flags register), instructions for them were considered different (LDA, LDX, & LDY, for load for instance) where in other instruction sets (for chips with multiple general purpose registers) they might be considered the same instruction affecting a different register, though considering them the same instruction didn't reduce the opcode count just the instruction group count. (Apologies for failing to keep my inner pendant properly inner!)
- thristian 3y agoThe original 6502 had exactly 151 opcodes, the same as the number of pokémon in the original Pokémon games.
- dspillett 3y agoThis is a wonderful useless fact. Thanks!
- gabrielsroka 3y ago> pendant I assume you mean pedant.
- dspillett 3y agoAuto-carrot strikes again… I really must stop writing things on the phone. I'm bad enough with a decent keyboard, sometimes I make sense at all via phone input.
- gabrielsroka 3y agoI meant instructions/mnemonics. I was referencing Simonw's post: > Here are the 65 hardcoded opcodes