Z80compatible

Z80compatible refers to CPUs or microcontrollers designed to execute software written for the Zilog Z80 by implementing a Z80-compatible instruction set architecture. The term is used for processors that aim for binary compatibility, letting programs built for the Z80 run with little or no modification.

The Z80 instruction set is 8-bit, with 8-bit registers (A, F, B, C, D, E, H, L), combined register pairs (AF, BC, DE, HL), a 16-bit stack pointer and program counter. It adds 16-bit index registers IX and IY, an I interrupt vector, and an R refresh counter; instruction prefixes like CB for bit operations. The Z80 is an extension of the 8080, offering more registers and instructions, better interrupt handling, and versatile I/O mechanisms, which contributed to its widespread adoption in the late 1970s and 1980s.

Not all Z80-compatible devices are exact clones. Some provide full binary compatibility and identical timing, while others offer a subset or include additional instructions, peripherals, or different cycle timings. In some cases, software must account for minor differences in I/O behavior or interrupt handling. The term often covers both faithful implementations and improved, backward-compatible variants.

Notable Z80-compatible lines include the Zilog Z80 family itself, and descendants such as the Z80-based Z180 and the eZ80, which add on-chip peripherals and faster operation while remaining binary-compatible with the Z80. The Game Boy’s LR35902 is a widely cited Z80-derived CPU used in handheld games, offering high performance with certain architectural deviations. In modern contexts, FPGA cores and emulation projects frequently model the Z80 ISA for compatibility and educational purposes.