DEX is an opcode for the 6502 processor. It decreases the value in the X register by 1. If the register contains zero before this instruction is executed, its value will wrap around so that it contains 255 (equivalent to -1 in 8-bit 2's complement arithmetic).

The N and Z flags may be affected by this instruction's execution.

The machine code representation of this opcode is 0xCA.

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