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Instruction Set Overview OpCode Matrix Instruction Details


Each opcode has an associated color which represents the flag (combination) that is available to that opcode. Because of this, I only need to connect a single flag-bit to the controller, which saves address/input bits in order to be able to have a full 8-bit opcode input. The single flag-input-bit is selected with a 3-to-8 multiplexer from all the available flags. The control bits for the multiplexer are the three most significant bits of the opcode.

Color/Opcode range Available flag (combination)
001xxxxx ZF
001xxxxx CF
010xxxxx NF
011xxxxx VF
100xxxxx NF ⊕ VF
101xxxxx (NF ⊕ VF) ∨ ZF
110xxxxx CF ∨ ZF
111xxxxx not assigned yet