Zilog Z-80
The Zilog Z80 is an 8-bit microprocessor introduced in 1975.
It implements an upward-compatible extension of the Intel 8080 instruction set, and requires only a +5 V supply. It adds several registers, a vectored interrupt system, and a hardware DRAM refresh counter to the 8080 architecture.
There were several speed grades, initially starting at 2.5 MHz (non-suffix) / 4 MHz (Z80A) / 6 MHz (Z80B), etc., later CMOS versions up to 20 MHz, and derivatives up to about 50 MHz. Several second-source manufacturers produced their versions of this CPU.
The National Semiconductor NSC800 is code-compatible with the Z-80 but has a multiplexed address/data bus like the Intel 8085, without being pin compatible with either.
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