27 Facts About Z80

Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product.

The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975.

Z80 came about when physicist and engineer Federico Faggin left Intel at the end of 1974 to found Zilog with Ralph Ungermann.

These companies were chosen because they could do the ion implantation needed to create the depletion-mode MOSFETs that the Z80 design used as load transistors in order to cope with a single 5-volt power supply.

Masatoshi Shima designed most of the microarchitecture as well as the gate and transistor levels of the Z80 CPU, assisted by a small number of engineers and layout people.

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Z80 took over from the 8080 and its offspring, the 8085, in the processor market and became one of the most popular and widely used 8-bit CPUs.

Programming model and register set of the Z80 are fairly conventional, ultimately based on the register structure of the Datapoint 2200.

The Z80 was designed as an extension of the Intel 8080, created by the same engineers, which in turn was an extension of the 8008.

The 16-bit IX and IY registers in the Z80 are primarily intended as base address-registers, where a particular instruction supplies a constant offset that is added to the previous values, but they are usable as 16-bit accumulators, among other things.

The Z80 introduced a new signed overflow flag and complemented the fairly simple 16-bit arithmetics of the 8080 with dedicated instructions for signed 16-bit arithmetics.

Instructions LD A, R and LD A, I affect the Z80 flags register, unlike all the other LD instructions.

The Z80 syntax uses parentheses around an expression to indicate that the value should be used as a memory address, while the 8086 syntax uses brackets instead of ordinary parentheses for this purpose.

Z80 uses 252 out of the available 256 codes as single byte opcodes; the four remaining codes are used extensively as opcode prefixes: CB and ED enable extra instructions, and DD or FD select IX+d or IY+d respectively (in some cases without displacement d) in place of HL.

Arithmetic instructions on the Z80 set it to indicate overflow rather than parity, while bitwise instructions still use it as a parity flag.

Z80 has six new LD instructions that can load the DE, BC, and SP register pairs from memory, and load memory from these three register pairs—unlike the 8080.

However, it was not until the fully pipelined eZ80 was launched in 2001 that those instructions finally became approximately as cycle-efficient as it is technically possible to make them, i e given the Z80 encodings combined with the capability to do an 8-bit read or write every clock cycle.

However, as they are not part of the formal definition of the instruction set, different implementations of the Z80 are not guaranteed to work the same way for every undocumented opcode.

Furthermore, the Z80 has a single instruction that will execute the entire loop.

One central example of this is that, for opcode fetch, the Z80 combines two full clock cycles into a memory access period.

However, this relation has slowly changed during the last decades, particularly regarding SRAM; cacheless, single-cycle designs such as the eZ80 have therefore become much more meaningful recently.

Also, several clones of Z80 were created in the Soviet Union, notable ones being the T34BM1, called ??1858??1.

The Z80-derived Z8S180 found its way into an early pen-operated personal digital assistant, the Amstrad PenPad PDA600 in 1993.

Zilog Z80 has long been a popular microprocessor in embedded systems and microcontroller cores, where it remains in widespread use today.

Applications of the Z80 include uses in consumer electronics, industrial products, and electronic musical instruments.

For example, Z80 was used in the groundbreaking music synthesizer Prophet-5, as well as in the first MIDI synthesizer Prophet 600.

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Z80 was used in the Sega Master System and Sega Game Gear consoles.

The TI-84 Plus CE series, introduced in 2015, uses the Z80-derived Zilog eZ80 processor and is still in production as of 2020.