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Revision as of 12:36, 3 June 2011 by Edward (talk | contribs) (more control bus lines HALT, WAIT, INT, NMI)
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  • This article is about the CPU chip used in the Spectrum. For the emulator snapshot format see Z80 format

The Zilog Z80A is the CPU used in the ZX80, ZX81 and all ZX Spectrum models, as well as most Spectrum clones and several other 8-bit micros. In the Spectrum, the Z80 is clocked at around 3.5MHz (for precise values see individual model pages).

Instruction Set


The Z80 has a 16-bit address bus and an 8-bit data bus. The control bus pins (all of which are active low) are:

Pin Description
/MREQ Memory Request
/IORQ I/O Request
/RD Read
/WR Write
/RFSH DRAM Refresh
/M1 Opcode Fetch Cycle
/HALT CPU Halted
/INT Maskable Interrupt
/NMI Non-Maskable Interrupt
/BUSRQ Bus (DMA) request
/BUSACK Bus (DMA) acknowledgement


Z80 chips are still available new, due largely to their continued popularity for embedded systems. Component suppliers such as Farnell and Rapid usually have them in stock.