The 8-bit and 16-bit processor era (1970s - 1980s) was marked by rapid advancements in microprocessor technology. These processors formed the core of personal computers, gaming consoles, and embedded systems, shaping the early days of the computing revolution. Below, we explore key processors of the era, their capabilities, and the impact they had on computing.
The 8080 processor, released by Intel in 1974, was an 8-bit microprocessor that followed on from the 8008, the first 8-bit processor which came after the 4004 IC.
The 8080 powered early computers and video games such as Midway Space Invaders.
The 6800, released by Motorola in 1974, was an 8-bit processor that featured a more advanced design compared to the 6502. It was used in early home computers and embedded systems. The 6800 introduced an improved instruction set and more powerful addressing modes, setting the stage for its more advanced sibling, the 6809.
The 6502, introduced by MOS Technology in 1975, was an 8-bit processor used in a wide range of devices. It became highly popular in personal computers and video game consoles due to its affordability and performance. Its simple architecture and efficient instruction set made it ideal for low-cost systems.
The design was inspired by the 6800 but was not compatible with it and rapidly gained popularity due to its low cost.
The Z80 processor, introduced by Zilog in 1976, was highly compatible with the Intel 8080 but with several enhancements. It had more registers and better support for interrupts, making it more powerful for computing tasks. The Z80 was used in the popular TRS-80, Sinclair ZX Spectrum, MSX and various arcade games.
The 8088, introduced by Intel in 1979, was a variant of the 8086 with an 8-bit external data bus. It powered the original IBM PC and was notable for its compatibility with existing 8-bit hardware. Despite its 16-bit architecture internally, the 8088's 8-bit bus reduced costs while providing good performance for early personal computers.
Due to being chosen to power the first IBM PC, it rapidly gained popularity and set the stage for future development of the i86 series which in its modern 64-bit multi-core variants powers servers, desktops, and laptops globally, making it one of the most important processors of the era.
The 68000 processor, released by Motorola in 1979, was a major leap forward as a 16-bit processor with a 32-bit internal architecture. It introduced a more powerful address bus, enabling access to 16 MB of memory. The 68000 became widely used in personal computers like the Apple Macintosh, Commodore Amiga, and Atari ST.
The need for processors for calculators, industrial controllers, keyboard controllers, etc., led to the development of the MCU in many guises.
| Computer / Console | Year Released | Processor | RAM | ROM | Disk Storage |
|---|---|---|---|---|---|
| Magnavox Odyssey | 1972 | None (Discrete logic) | None | None | None |
| Atari 2600 | 1977 | MOS 6507 @ 1.19 MHz | 128 bytes | 4 KB (cartridge) | None |
| Intellivision | 1979 | GI CP1610 @ 894 kHz | 1 KB | 4 KB | None |
| ColecoVision | 1982 | Zilog Z80A @ 3.58 MHz | 1 KB | 8 KB | None |
| Nintendo Entertainment System (NES) | 1983 | Ricoh 2A03 (6502 core) @ 1.79 MHz | 2 KB | 32 KB (cartridge) | None |
| Sega Master System | 1985 | Zilog Z80 @ 3.58 MHz | 8 KB | 16 KB BIOS + cartridge | None |
Note: The specifications for some systems, such as early home computers, were quite minimal, and many systems used cassette tapes for storage due to the lack of affordable disk drives. As technology progressed, disk storage and more powerful processors became the standard for personal computers and gaming consoles.
The 6502, 6800, and 6809 microprocessors are among the most influential early CPUs, used in a wide range of computing systems from home computers to embedded devices. Below is an overview of each processor, followed by a feature comparison:
The MOS Technology 6502 was an 8-bit microprocessor introduced in 1975. It became widely popular in early home computers and gaming consoles, such as the Apple II, Commodore 64, and Atari consoles.
Variants of the 6502 include the WDC 65C02 (CMOS version) and the WDC 65C816 (a 16-bit extension), providing enhanced features like lower power consumption, higher speeds, and improved functionality.
The Motorola 6800 was an 8-bit microprocessor released in 1974. It is known for its use in embedded systems, early personal computers, and gaming systems. The 6800 was the basis for later, more advanced processors such as the 6809. It was also used in the design of several early home computers like the Tandy TRS-80 and the Motorola M6800 development systems.
Variants of the 6800 include the 6802 (low-power version), 6804 (cost-reduced), and 6801 (microcontroller variant), with each offering specific optimizations for embedded and industrial applications.
The Motorola 6809 was introduced in 1978 and is a more advanced version of the 6800. It is known for its rich instruction set, powerful 16-bit operations, and highly efficient addressing modes. The 6809 was widely used in systems like the Tandy Color Computer, Dragon 32, and various embedded systems.
Variants of the 6809 include the 6809E (enhanced version with better power efficiency), the 6309 (featuring hardware multiply and divide instructions), and the 68HC09 (with integrated peripherals for embedded applications).
| Feature | 6502 | 6800 | 6809 |
|---|---|---|---|
| Introduction Year | 1975 | 1974 | 1978 |
| Data Bus | 8-bit | 8-bit | 8-bit (16-bit operations) |
| Address Bus | 16-bit | 16-bit | 16-bit |
| Instruction Set | Simple, efficient | Moderately complex | Advanced, rich addressing modes |
| Clock Speed | 1 MHz to 2 MHz | 1 MHz to 2 MHz | 1 MHz to 2.5 MHz |
| Registers | 3 8-bit general-purpose, 1 status | 2 8-bit general-purpose, 1 status | 8 8-bit general-purpose, 1 status |
| Interrupts | 2 interrupt lines | 2 interrupt lines | 5 interrupt lines |
| Variants | 65C02 (CMOS), 65C816 (16-bit) | 6802, 6804, 6801 | 6809E, 6309, 68HC09 |
| Common Uses | Home computers, gaming consoles | Embedded systems, early personal computers | Embedded systems, home computers (e.g., Tandy Color Computer) |
| Peripheral Integration | External peripherals required | External peripherals required | More advanced, built-in peripherals (e.g., serial I/O, timers) |
The 6502, 6800, and 6809 powered many iconic home computers, arcade systems, and embedded platforms across the late 1970s and 1980s. Many of these systems defined the early personal computing era.
These microprocessors supported a variety of operating systems, ranging from monitor ROMs and BASIC interpreters to full multitasking OSes like OS-9. Below is a list of notable operating systems used on each CPU family.
The 6809 stands out historically for supporting OS-9, one of the most capable operating systems of the early 1980s, offering memory protection, multitasking, and multi-user features normally found only on minicomputers.
Note: The 6809 is considered to be more powerful than both the 6502 and 6800 due to its advanced instruction set, better support for 16-bit operations, and more sophisticated addressing modes. It also features more interrupt lines and advanced peripherals, making it suitable for complex embedded systems.
The Intel 8080 and 8085 are 8-bit microprocessors introduced in the 1970s. These processors played a crucial role in the early development of microcomputing.
The Intel 8080, released in 1974, was one of the first widely-used microprocessors. It was used in early computers and control systems.
The Intel 8085, introduced in 1976, was an improved version of the 8080 with simplified power requirements and better performance.
The Z80 is an 8-bit microprocessor designed and manufactured by Zilog in 1976. It was widely used in early personal computers and embedded systems.
Several devices based on the Z80 were developed for MSX computers, visit the MSX page for more details.
The Intel 8080, Intel 8085, and Zilog Z80 are all microprocessors that played a crucial role in the early development of computer systems. Here's a comparison of their features:
| Feature | Intel 8080 | Intel 8085 | Zilog Z80 |
|---|---|---|---|
| Introduction Year | 1974 | 1976 | 1976 |
| Data Bus | 8-bit | 8-bit | 8-bit |
| Address Bus | 16-bit | 16-bit | 16-bit |
| Addressable Memory | 64 KB | 64 KB | 64 KB |
| Instruction Set | Basic | Improved (with 8080 compatibility) | More extensive (includes 8080 & new instructions) |
| Registers | 6 8-bit general-purpose registers | 6 8-bit general-purpose registers, 16-bit stack pointer | 8-bit and 16-bit general-purpose registers, alternate register set |
| Clock Speed | 2 MHz | 3 MHz (up to 5 MHz in some versions) | 4 MHz (up to 20 MHz in some versions) |
| Interrupts | 5 interrupts | 5 interrupts (with priority levels) | 12 interrupts (with more flexible prioritization) |
| Power Consumption | High | Low | Moderate |
| Peripherals | External peripherals required | Built-in serial I/O | Zilog serial I/O, DMA, Counter timers, PIO and other peripheral chips available which support the Z80 vectored interrupt structure Newer variants have substantial onboard peripherals for embedded applications MSX computer chips were developed around the Z80 processor which integrates the majority of the onboard circuitry required to implement the MSX standard |
| Compatibility | None | Compatible with 8080 | Fully backward compatible with 8080 and 8085 |
The Intel 8080, Intel 8085, and Zilog Z80 powered many influential early computers. The Z80 in particular became the heart of the home computer revolution in the 1980s, especially through the ZX Spectrum and MSX platforms.
Because of its enhanced instruction set and additional registers, the Z80 dominated home computing, education, and CP/M business machines throughout the 1980s.
The most important OS for the 8080, 8085, and early Z80 systems. Written originally for the 8080 but ran extremely well on the Z80 due to backward compatibility.
Microsoft’s CP/M-compatible OS for MSX computers. Provided:
The Spectrum used a built-in BASIC interpreter OS stored in ROM:
Very lightweight ROM-based OS with integer BASIC interpreter and extremely low memory overhead.
Used on TRS-80 systems, provided:
Many development boards and embedded systems did not run a full OS. Instead, they used:
The Intel processors from the 8086 to the 80486 were pivotal in the development of personal computing. They marked significant advances in microprocessor design, offering increasing clock speeds, wider data paths, and advanced memory management. Below, we will explore the key features and differences of these processors, followed by a comparison table.
The Intel 8086 was released in 1978 as a 16-bit microprocessor and is often regarded as the predecessor to the x86 architecture. It was designed with a 16-bit data bus and 20-bit address bus, allowing it to access up to 1 MB of memory. The 8086 became widely known for being the basis of the IBM PC.
The Intel 8088 is very similar to the 8086, but it features an 8-bit external data bus rather than the 8086's 16-bit data bus. This made the 8088 less expensive to produce and allowed it to be used in the original IBM PC, where it became famous for its low cost and simplicity.
The Intel 80186 was an enhanced version of the 8086, introduced in 1982. It included additional features such as built-in peripherals (timer, interrupt controller, etc.) and a more advanced instruction set. However, it was not widely adopted in PCs, as the 80286 was released shortly thereafter.
The Intel 80188 is a variant of the 80186 that uses an 8-bit external data bus. It provided similar advantages to the 8088 over the 8086, offering lower cost and easier integration into systems with 8-bit buses. However, like the 80186, it was less widely adopted in the personal computer market.
The Intel 80286, released in 1982, was a major leap forward in performance and capability. It featured a 16-bit data bus and 24-bit address bus, which allowed it to address up to 16 MB of memory. The 80286 introduced protected mode, allowing for better multitasking and memory management, a feature that laid the groundwork for modern operating systems.
The Intel 80386, introduced in 1985, was the first true 32-bit microprocessor in the x86 family. It featured a 32-bit data bus and 32-bit address bus, which allowed it to address up to 4 GB of memory. The 80386 also introduced a new virtual memory system and further enhanced multitasking capabilities, which made it the foundation for the development of modern operating systems like Windows NT.
The Intel 80486, released in 1989, was a significant upgrade to the 80386, incorporating a built-in math coprocessor (FPU) and higher clock speeds. It featured a 32-bit data bus and 32-bit address bus and was widely used in desktop computers. The 80486 was the first processor to achieve true "superscalar" architecture, allowing for the execution of multiple instructions per clock cycle, which greatly increased performance.
| Feature | 8086 | 8088 | 80186 | 80188 | 80286 | 80386 | 80486 |
|---|---|---|---|---|---|---|---|
| Introduction Year | 1978 | 1979 | 1982 | 1982 | 1982 | 1985 | 1989 |
| Data Bus | 16-bit | 8-bit | 16-bit | 8-bit | 16-bit | 32-bit | 32-bit |
| Address Bus | 20-bit | 20-bit | 20-bit | 20-bit | 24-bit | 32-bit | 32-bit |
| Max Memory Addressable | 1 MB | 1 MB | 1 MB | 1 MB | 16 MB | 4 GB | 4 GB |
| Protected Mode | No | No | No | No | Yes | Yes | Yes |
| Superscalar | No | No | No | No | No | No | Yes |
| Floating Point Unit (FPU) | No | No | No | No | No | No | Yes |
| Clock Speed | 5-10 MHz | 4-8 MHz | 6-10 MHz | 6-10 MHz | 6-25 MHz | 12-40 MHz | 20-100 MHz |
These Intel processors powered many influential personal computers, workstations, and early business systems. Below are some well-known examples associated with each processor generation:
The x86 processors from the 8086 through the 80486 supported a wide range of operating systems over the years. Some were simple command-line OSes designed for early PCs, while others were advanced multitasking systems that introduced features still used today.
BeOS was introduced slightly later but still ran on fast 486 and early Pentium systems.
The evolution of operating systems closely followed the capabilities of these Intel processors, especially the transition to protected mode on the 286 and full 32-bit multitasking on the 386.
Note: The 80486 represented a major leap in performance over the 80386, incorporating integrated floating-point operations (FPU) and the ability to execute multiple instructions per clock cycle, making it the foundation for more advanced microprocessors.
The Motorola 68000, introduced in 1979, is a 16/32-bit CISC microprocessor that launched an entire family of processors (68010, 68020, 68030, 68040, 68060). It powered many of the most influential computers of the 1980s and 1990s, including the Apple Macintosh, Commodore Amiga, Atari ST, and numerous arcade boards.
The 68000 combines a 16-bit external bus with a 32-bit internal architecture and a flat 24-bit address space, giving it a powerful instruction set far ahead of other microprocessors of its time.
The original Motorola 68000 (MC68000) is known for its elegant and orthogonal instruction set, large register file, and high performance relative to contemporary 8-bit and early 16-bit CPUs. It became the foundation of the m68k CPU family used widely in personal computers, workstations, game consoles, and embedded systems.
Variants include the 68008 (8-bit external bus), 68010 (improved exception handling), and the widely used 68020–68060 series offering true 32-bit processing, integrated MMUs, FPUs, and higher clock speeds.
| Feature | Motorola 68000 |
|---|---|
| Introduction Year | 1979 |
| Internal Architecture | 32-bit |
| External Data Bus | 16-bit |
| Address Bus | 24-bit (16 MB address space) |
| Registers | 16 × 32-bit registers (8 data, 8 address) |
| Instruction Set | Orthogonal 32-bit CISC |
| Clock Speeds | 4 MHz, 8 MHz, 12 MHz, 16 MHz |
| Variant CPUs | 68008, 68010, 68020, 68030, 68040, 68060 |
| Common Uses | Home computers, workstations, arcade boards, embedded systems |
The 68000 family supported some of the most advanced and influential operating systems of the 1980s and 1990s, ranging from GUIs to multitasking UNIX-like systems.
The 68000 was unique in this era for supporting both classic GUI operating systems (Mac, AmigaOS, TOS) and full UNIX workstations, a range unmatched by most contemporary CPUs.
The Motorola 68000 family had a major impact on computing history, powering early GUI computers, professional workstations, and a generation of game consoles and arcade systems. Its clean instruction set and large register model influenced later architectures, including ARM.
The Intel 8035 is an 8-bit microprocessor introduced in 1976 as a part of the 8030 series. It was designed primarily for embedded control applications. The 8035 shares a similar architecture with the Intel 8080, but it lacks the general-purpose registers, making it less flexible than the 8080. It was used in a variety of early embedded systems and devices.
Features:
The National Semiconductor IMP-16 is an early 8-bit microprocessor introduced in 1975. It was notable for being one of the first processors to use the new "microprocessor" architecture. While not as widely used as the 8080 or 6502, it found use in some embedded systems.
Features:
The Motorola 6801, released in 1977, is an 8-bit microprocessor that features the same general architecture as the 6800 but with added flexibility. It was widely used in embedded systems, automotive, and consumer electronics, particularly because it had integrated I/O features that reduced the need for external peripherals.
Features:
The RCA 1802 is an 8-bit microprocessor introduced in 1976, famous for its use in the early space applications, particularly in spacecraft. It features a highly efficient, low-power design that made it ideal for applications where heat dissipation and energy efficiency were crucial.
Features:
The Fairchild F8 was introduced in 1975 and was used in early embedded systems, particularly in telecommunications and consumer electronics. It was a 40-pin microprocessor with a 4-bit wide ALU (Arithmetic Logic Unit) and a register-based architecture.
Features:
The Signetics 2650, released in 1975, was another early 8-bit processor designed for embedded systems. Unlike other processors of the time, the 2650 was designed with a highly flexible interrupt handling system, making it an ideal choice for real-time processing applications.
Features:
The Transputer was a pioneering family of microprocessors developed by Inmos in the 1980s, designed for parallel computing. Unlike traditional microprocessors, Transputers integrated processing power with on-chip memory and communication links, allowing multiple processors to be connected in a network. This innovative architecture enabled the creation of large, distributed parallel computing systems for high-performance applications.
The Transputer family was built on a 32-bit RISC architecture, with models such as the T414, T800, and T225 offering varying levels of processing power and communication capabilities. The processors supported multiple communication links, enabling them to communicate with other Transputers in a network, facilitating massively parallel computation.
Transputers were mainly programmed using the occam programming language, designed specifically for concurrent and parallel systems. These processors found applications in real-time processing, scientific simulations, image processing, and early-stage artificial intelligence.
While the Transputer family was eventually discontinued, its innovative design influenced modern multi-core processors and parallel computing systems, laying the groundwork for the distributed computing technologies we use today.
Transputer processors are a family of microprocessors developed by Inmos (a British semiconductor company) in the 1980s. These processors were created specifically for parallel computing, with the goal of providing high-performance systems by integrating multiple processors in a network. Their architecture made them well-suited for scientific, engineering, simulation, and real-time applications.
The transputer architecture was one of the first to feature integrated communication links between processors, allowing them to be connected in flexible topologies such as pipelines, rings, meshes, and hypercubes. A transputer combined a CPU, RAM, and high-speed communication links on a single chip, which was revolutionary for the time. This made it possible to design parallel computing clusters that scaled linearly simply by adding more transputers.
Several transputer models were released across multiple generations:
Transputers were used in a wide range of computers, workstations, accelerator boards, and supercomputing systems. Key examples include:
ISA and later VME cards containing multiple interconnected T4xx or T8xx processors. Used in universities, labs, and early parallel research systems.
A modular transputer-based supercomputer used in academia, intelligence agencies, and defense research. Systems ranged from a few dozen to several thousand transputers.
German-made high-end parallel computers that scaled to thousands of T800 processors. Models included:
Industrial modules embedding T400/T800 processors for robotics, automation and real-time control systems.
A workstation planned by Atari in the late 1980s, built around the T800 and intended to run the Helios OS. Prototype units exist, but commercial release was cancelled.
Companies like SGS, Meiko, and Transtech produced transputer-based image accelerators for medical imaging, video processing and early VR research.
Some early Connection Machine research systems experimented with transputers before moving to custom silicon.
Several operating systems were developed specifically to support parallel execution on transputers:
A programming language and runtime system for concurrency. It directly matched the hardware communication model of transputers.
-- Simple OCCAM example demonstrating parallel processes
PROC adder(CHAN OF INT in1, CHAN OF INT in2, CHAN OF INT out)
INT a:
INT b:
SEQ
in1 ? a -- read from first channel
in2 ? b -- read from second channel
out ! (a + b) -- send sum to output channel
:
PROC main()
CHAN OF INT c1, c2, c3:
PAR
SEQ
c1 ! 10
c2 ! 32
adder(c1, c2, c3)
SEQ
INT result:
c3 ? result
-- result now contains 42
:
Transputers were also supported by the C programming language
/* Example Transputer C code using INMOS iC compiler */
#include <occamio.h>
/* Channels are represented as pointers to channel ends */
CHAN_INT inChan;
CHAN_INT outChan;
void adder()
{
int a, b;
in(&inChan, &a); /* read integer from channel */
in(&inChan, &b);
int sum = a + b;
out(&outChan, sum); /* write result */
}
void main()
{
int x = 7, y = 9;
out(&inChan, x);
out(&inChan, y);
adder();
int result;
in(&outChan, &result);
/* result now holds 16 */
}
A lightweight operating environment for debugging, loading, and running occam programs across transputer networks.
The most advanced transputer OS, developed by Perihelion Software. Features included:
A distributed OS and message-passing system designed for Parsytec transputer supercomputers. Highly optimized for T800 FP performance.
A Unix-like research OS designed for virtual channel systems and early T9000 prototypes.
A small multitasking OS ported to transputer arrays and used in embedded and industrial systems.
The transputer was a major milestone in the evolution of parallel computing. Although commercial adoption declined in the 1990s, ideas from the architecture directly influenced:
The Intel 8031, introduced in 1976, is an 8-bit microcontroller that comes with onboard ROM and RAM. It was designed for embedded applications requiring program memory (ROM) and data memory (RAM) in a single chip. The 8031 was used in a wide variety of embedded systems, from control systems to consumer electronics.
Features:
The Intel 8051, introduced in 1980, is an 8-bit microcontroller with both ROM and RAM on the same chip, making it ideal for embedded systems requiring standalone operation. It became one of the most popular MCU families due to versatility and many derivative chips.
Features:
The Atmel AT89C51, introduced in the 1990s, is a derivative of the Intel 8051, with onboard Flash memory for program storage. It allows easy updates of the program memory without replacing the chip.
Features:
The Microchip PIC16F84, introduced in 1993, is an 8-bit microcontroller with onboard Flash memory. Popular for its small size, low cost, and ease of use, it became widely used in embedded systems and hobbyist projects.
Features:
The Atmel ATtiny85 is an 8-bit microcontroller with both EEPROM and Flash memory onboard. Introduced in the mid-2000s, it gained popularity in the maker community for its small form factor and simplicity.
Features:
The Motorola MC68HC11, released in 1985, is an 8-bit microcontroller with Flash memory for program storage, suitable for automotive and industrial control systems.
Features:
STMicroelectronics offers a wide range of MCUs suitable for many embedded applications. Below is a summary of three key families of ST MCUs with features and applications.
The ST6 series is an early generation of 8-bit microcontrollers for basic embedded systems. It has a simple architecture with essential peripherals, ideal for cost-sensitive and low-power applications.
The ST7 series builds upon the ST6 with higher memory capacity, improved peripherals, and low-power support. Ideal for advanced embedded systems requiring performance and efficiency.
The STM8 series represents a leap forward with an 8-bit core optimized for high performance. Widely used from consumer electronics to industrial control, STM8 offers extensive memory, peripherals, and advanced I/O.
The NEC μPD75xx series, launched in the late 1980s, are 8-bit microcontrollers with on-chip Flash memory. Used in embedded systems, home appliances, and automotive control.
Features:
The Z80 PIO (Parallel Input/Output) provides two independent 8-bit ports (Port A and Port B), each with its own mode control register.
Each port supports interrupt-on-change, vectorized interrupts, and handshake control lines. Used in printers, keypads, memory-mapped port expanders, robotics, and CP/M workstation peripherals.
The Z80 CTC provides four independent timer/counter channels, each capable of operating in:
Capable of baud-rate generation, periodic interrupts, triggering DMA transfers, and precise event timing. Strongly associated with the SIO and DART to create full communications subsystems.
The Z80 DART (Dual Asynchronous Receiver/Transmitter) implements two independent UARTs with fine-grained configuration:
Used in early CP/M terminals, industrial serial networks, and point-of-sale systems.
The Z80 SIO extends the DART by adding synchronous protocols:
Used in X.25 packet switchers, telecom gear, early networking nodes, and bank terminals.
The Z80 DMA allows block transfers without CPU involvement, supporting:
Used in floppy controllers, disk buffer systems, video memory refreshers, and high-speed acquisition hardware.
The Z80 KIO integrates peripheral functions:
This single-chip peripheral hub reduced board size in embedded Z80 appliances, terminals, and portable devices.
The SCC (Serial Communications Controller) is one of the most advanced Z80 peripherals. Features include:
Used in early routers, PBX systems, WAN cards, and SNA/X.25 controllers.
The CIO integrates timers and flexible I/O control:
Used in telecommunications racks, control boards, and multifunction I/O backplanes.
The Z84C90 integrates:
The tight integration reduces bus latency and simplifies PCB designs for multi-I/O Z80 systems.
The Z8470 offers:
Popular in industrial controllers, robotics, and Z80 bus expansion modules.
The Z80 has one of the most flexible interrupt systems of any 8-bit processor, supporting three distinct interrupt modes:
The CPU treats the interrupting device as if it executed an opcode on the data bus. This allows hardware devices to inject a single-byte instruction (typically RST N). Rarely used in simple systems but powerful for multi-device interrupt handlers.
The simplest mode: any maskable interrupt forces a jump to address 0038h.
Used on Sinclair ZX Spectrum, MSX 1, ColecoVision, and many arcade boards.
The Z80's most unique feature: a fully table-driven interrupt vector system similar to modern CPUs.
This allows:
IM2 was widely used in MSX computers, many Z80 industrial controllers, and advanced CP/M systems.
Provides three 8-bit ports (A, B, C) configurable as input/output:
Used for serial communication with configurable baud rate:
Used for timing, event counting, and frequency generation:
Supports prioritized interrupt handling for CPU:
Manages key scanning and 7-segment display output:
Provides high-speed memory-peripheral transfers without CPU intervention:
Used for general-purpose I/O in industrial applications:
Combines RAM, timers, and GPIO in one IC:
Similar to 8237 but for Intel 8085/8086 memory systems:
Provides stable clock signals and reset to CPU/peripherals:
The MC6820 provides two 8-bit bidirectional ports. Features:
Used in early 6800-based computers and embedded I/O boards.
The MC6821 improves upon the 6820 with more robust control lines and timing. Key features:
Common in industrial control and early home computer systems.
Supports asynchronous serial data transfers. Features include:
Used for connecting terminals, modems, and serial devices to 6800 systems.
Contains three independent 16-bit timers. Features:
Found in 6800-based computers and embedded timing applications.
The MC6845 generates screen addresses and timing for raster displays:
Used as small on-chip buffers for peripherals. Features:
Provides basic 8-bit I/O capabilities. Features:
Rare peripheral used in research boards:
Combines a 16-bit timer and two 8-bit I/O ports:
The MC68681 provides two serial channels plus timers. Features:
Provides two bidirectional 8-bit ports with handshake control:
Enhanced I/O with timers and shift registers:
Used in Commodore 64, Apple II, and Atari systems.
Features include:
Used in Atari 2600 and similar systems:
Integrated I/O, timers, and serial control:
Generates memory addresses for video display:
Used in Atari 2600 console:
Basic input/output interface for simple peripherals.
Used in games or security applications to provide random data.
Integrated waveform generator with GPIO capabilities:
3-channel PSG with 8-bit GPIO port lines:
Interface for floppy drives with interrupt and DMA signals:
Provides keyboard scanning, translation, and control logic:
Provides hardware floating-point arithmetic for 68000-series CPUs:
Used in MSX and ColecoVision consoles:
Standard controller in IBM PC/AT compatible systems:
Provides two serial channels and programmable I/O lines:
Used in arcade and game console systems for graphics and control I/O.
Designed for RCA 1802 microprocessor systems with simple GPIO functions.
Drop-in replacement for 6520 with CMOS low-power and enhanced timing.