Bitmask

State Machines: Why Bitwise is Best A State Machine manages the status of a system (e.g., a game character is ‘Jumping’, ‘Firing’, or ‘Hit’). In high-level languages, you might use three separate Boolean variables for these. In Z80 assembly, that’s inefficient. By using a single register (like C) as a status register, you can manage up to eight independent Boolean flags, dedicating one bit to each status. This is the fastest method for context management. ...

Logic Operations: AND, OR, and XOR These instructions perform bitwise logic operations between the Accumulator (A) and a source (another register or immediate value), storing the result back in A. They are crucial for filtering or combining specific data flags. The Core Logic Commands: Instruction Action Purpose AND N Bitwise AND (A = A & N) Filtering/Masking: Clears (forces to 0) any bits in A that are 0 in N. OR N Bitwise OR (A = A | N) Setting: Sets (forces to 1) any bits in A that are 1 in N. XOR N Bitwise XOR (A = A ^ N) Toggling: Flips the state (0→1, 1→0) of any bits in A that are 1 in N. Example: Filtering a Status Register If we only care about the highest two bits of a status register read into A: ...