The Zilog Z280 is a

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

, an enhancement of the

Zilog Z80 The Z80 is an 8-bit computing, 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. The first wor ...

architecture, introduced in July 1987. It is basically the Z800, renamed, with slight improvements such as being fabricated in CMOS. It was a commercial failure. Zilog added a

memory management unit A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit having all memory references passed through itself, primarily performing the translation of virtual memory addresses to physical ...

(MMU) to expand the addressing range to 16 MB, features for multitasking and

multiprocessor Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There ar ...

and coprocessor configurations, and 256 bytes of on-chip static RAM, configurable as either a cache for instructions and/or data, or as part of the ordinary address space. It has a huge number of new instructions and

addressing mode Addressing modes are an aspect of the instruction set architecture in most central processing unit (CPU) designs. The various addressing modes that are defined in a given instruction set architecture define how the machine language instructions ...

s giving a total of over 2000 combinations. It is capable of efficiently handling 32-bit data operations including hardware multiply, divide, and sign extension. It offers Supervisor and User operating modes, and optionally separate address spaces for instructions and data in both modes (four total possible address spaces). Its internal

clock signal In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits. A clock s ...

can be configured to run at 1, 2 or 4 times the external clock's speed (e.g. a 12 MHz

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

with a 3 MHz

bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...

). Unlike the Z80 the Z280 uses a multiplexed arrangement for its address and data busses. More successful extensions of the Z80-architecture include the Hitachi HD64180 in 1986 and Zilog eZ80 in 2001, among others. See further Zilog Z800. The Z280 had many advanced features for its time, most of them never seen again on a Zilog processor: * On-chip instruction and/or data cache, or on-chip RAM *

Instruction pipelining In computer engineering, instruction pipelining or ILP is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing inco ...

* High performance 16-bit Z-BUS interface or 8-bit Z80-compatible bus interface * Built-in MMU with

memory protection Memory protection is a way to control memory access rights on a computer, and is a part of most modern instruction set architectures and operating systems. The main purpose of memory protection is to prevent a process from accessing memory that h ...

* Ability to determine which register set is in context with instructions JAF and JAR * Three on-chip 16-bit counter/timers * Four on-chip

DMA DMA may refer to: Arts * ''DMA'' (magazine), a defunct dance music magazine * Dallas Museum of Art, an art museum in Texas, US * Danish Music Awards, an award show held in Denmark * BT Digital Music Awards, an annual event in the UK * Doctor of M ...

channels * On-chip full duplex UART * User I/O

trap A trap is a mechanical device used to capture or restrain an animal for purposes such as hunting, pest control, or ecological research. Trap or TRAP may also refer to: Art and entertainment Films and television * ''Trap'' (2015 film), Fil ...

Supervisor mode In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security). Compute ...

( privileged instructions) * Illegal instruction trap * Coprocessor emulation

* Burst mode memory access *

Multiprocessor Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There ar ...

support, with many bus configuration modes * Support for multiple external coprocessors through an accelerated communication interface * Multiple I/O pages, which also allows for internal I/O devices without restricting the address range of the I/O ports like on eZ80, or conflicting with existing

motherboard A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...

devices, like the Z180. *

Stack overflow In software, a stack overflow occurs if the call stack pointer exceeds the stack bound. The call stack may consist of a limited amount of address space, often determined at the start of the program. The size of the call stack depends on many facto ...

warning

References

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References

Further reading