4-bit computing

4-bit computing is the use of computer architectures in which integers and other data units are 4 bits wide. 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses of that size. A group of four bits is also called a nibble and has 2⁴ = 16 possible values, with a range of 0 to 15.

Contents

• History
• Uses
• Details
• List of 4-bit processors
• See also
• References
• External links

4-bit processors were widely used in electronic calculators and other roles where decimal math was used, like electronic cash registers, microwave oven timers, and so forth. This is because a 4-bit value holds a single binary coded decimal (BCD) digit, making it a natural size for directly processing decimal values. As a 4-bit value is generally too small to hold a memory address for real-world programs or data, the address bus of these systems was generally larger. For instance, the canonical 4-bit microprocessor, the Intel 4004, had a 12-bit address format.

4-bit designs were used only for a short period when integrated circuits were still expensive, and were found primarily in cost-sensitive roles. While 4-bit computing is mostly obsolete, 4-bit values are still used in the same decimal-centric roles they were developed for, and modern implementations are generally much wider and process multiple 4-bit values in parallel. An example of such a system is the HP Saturn design of the 1980s. By the 1990s, most such uses had been replaced by general purpose binary designs.

History

A 4-bit processor may seem limited, but it is a good match for calculators, where each decimal digit fits into four bits. ^[1]

Some of the first microprocessors had a 4-bit word length and were developed around 1970. The first commercial microprocessor was the binary-coded decimal (BCD-based) Intel 4004, ^{[2] [3]} developed for calculator applications in 1971; it had a 4-bit word length, but had 8-bit instructions and 12-bit addresses. It was succeeded by the Intel 4040, which added interrupt support and a variety of other new features.

The first commercial single-chip computer was the 4-bit Texas Instruments TMS 1000 (1974). ^[1] It contained a 4-bit CPU with a Harvard architecture and 8-bit-wide instructions, an on-chip instruction ROM, and an on-chip data RAM with 4-bit words. ^[4]

The Rockwell PPS-4 was another early 4-bit processor, introduced in 1972, which had a long lifetime in handheld games and similar roles. It was steadily improved and by 1975 been combined with several support chips to make a one-chip computer. ^[5]

The 4-bit processors were programmed in assembly language or Forth, e.g. "MARC4 Family of 4 bit Forth CPU" ^[6] (which is now discontinued) because of the extreme size constraint on programs and because common programming languages (for microcontrollers, 8-bit and larger), such as the C programming language, do not support 4-bit data types (C, and C++, and more languages require that the size of the char data type be at least 8 bits, ^[7] and that all data types other than bitfields have a size that is a multiple of the character size ^{[8] [9] [10]} ).

The 1970s saw the emergence of 4-bit software applications for mass markets like pocket calculators. During the 1980s, 4-bit microprocessors were used in handheld electronic games to keep costs low.

In the 1970s and 1980s, a number of research and commercial computers used bit slicing, in which the CPU's arithmetic logic unit (ALU) was built from multiple 4-bit-wide sections, each section including a chip such as an Am2901 or 74181.

The Zilog Z80, although it is an 8-bit microprocessor, has a 4-bit ALU. ^{[11] [12]}

Although the Data General Nova is a series of 16-bit minicomputers, the original Nova and the Nova 1200 internally processed numbers 4 bits at a time with a 4-bit ALU, ^[13] sometimes called "nybble-serial". ^[14]

The HP Saturn processors, used in many Hewlett-Packard calculators between 1984 and 2003 (including the HP 48 series of scientific calculators) are "4-bit" (or hybrid 64-/4-bit) machines; as the Intel 4004 did, they string multiple 4-bit words together, e.g. to form a 20-bit memory address, and most of the registers are 64 bits wide, storing 16 4-bit digits. ^{[15] [16] [17]}

In addition, some early calculators – such as the 1967 Casio AL-1000, the 1972 Sinclair Executive, and the aforementioned 1984 HP Saturn  – had 4-bit datapaths that accessed their registers 4 bits (one BCD digit) at a time. ^[18]

Uses

One bicycle computer specifies that it uses a "4 bit, 1-chip microcomputer". ^[19] Other typical uses include coffee makers, infrared remote controls, ^[20] and security alarms. ^[21]

The processor in Barbie typewriters that can encrypt is a 4-bit microcontroller. ^[22]

Several manufacturers used 4-bit microcontrollers in their early electronic games: ^[23]

• Mattel's Funtronics Jacks, Red Light Green Light, Tag, Plus One and Dalla$.
• Milton Bradley Lightfight and Electronic Battleship 1982.
• Coleco Head to Head Basketball.
• National Semiconductor Quiz Kid Racer.
• Entex Space Invader.
• Texas Instruments My Little Computer. ^[24]

Western Digital used a 4-bit microcontroller as the basis for their WD2412 time-of-day clock. ^[25]

The Grundy Newbrain computer uses a 4-bit microcontroller to manage its keyboard, tape I/O, and its built-in 16 character VF alphanumeric display. ^[26]

Details

With 4 bits, it is possible to create 16 different values. All single-digit hexadecimal numbers can be written with four bits.

Binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by four bits.

List of 4-bit processors

• Intel 4004 (first 4-bit microprocessor from 1971, though Four-Phase Systems AL1 from 1969 is older, discontinued 1981)
• Intel 4040 (discontinued 1981)
• TMS 1000 (the first high-volume commercial microcontroller, from 1974, after Intel 4004; now discontinued)
• Atmel MARC4 core ^{[27] [28]} (discontinued because of Low demand. "Last ship date: 7 March 2015" ^[29] )
• Samsung S3C7 (KS57 Series) 4-bit microcontrollers (RAM: 512 to 5264 nibbles, 6 MHz clock)
• Toshiba TLCS-47 series
• HP Saturn
• NEC μPD75X
• NEC μCOM-4
• NEC (now Renesas) μPD612xA (discontinued), μPD613x, μPD6x ^{[20] [30]} and μPD1724x ^[31] infrared remote control transmitter microcontrollers ^{[32] [33]}
• EM Microelectronic-Marin EM6600 family, ^[34] EM6580, ^{[35] [36]} EM6682, ^[37] etc.
• Epson S1C63 family
• National Semiconductor "COPS I" and "COPS II" ("COP400") 4-bit microcontroller families ^[38]
• National Semiconductor MAPS MM570X
• Sharp SM590/SM591/SM595 ^{[39] : 26–34}
• Sharp SM550/SM551/SM552 ^{[39] : 36–48}
• Sharp SM578/SM579 ^{[39] : 49–64}
• Sharp SM5E4 ^{[39] : 65–74}
• Sharp LU5E4POP ^{[39] : 75–82}
• Sharp SM5J5/SM5J6 ^{[39] : 83–99}
• Sharp SM530 ^{[39] : 100–109}
• Sharp SM531 ^{[39] : 110–118}
• Sharp SM500 ^{[39] : 119–127} (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)
• Sharp SM5K1 ^{[39] : 128–140}
• Sharp SM4A ^{[39] : 141–148}
• Sharp SM510 ^{[39] : 149–158} (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)
• Sharp SM511/SM512 ^{[39] : 159–171} (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)
• Sharp SM563 ^{[39] : 172–186}

See also

• GMC-4
• Hitachi HD44780 LCD controller
• Intel's LPC (low-pin-count) bus/interface for 4-bit communication
  • Its successor for modern computers, Intel's Enhanced Serial Peripheral Interface (eSPI), allows 1-bit, 2-bit, and 4-bit communication

Related Research Articles

A microprocessor is a computer processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, and control circuitry required to perform the functions of a computer's central processing unit (CPU). The IC is capable of interpreting and executing program instructions and performing arithmetic operations. The microprocessor is a multipurpose, clock-driven, register-based, digital integrated circuit that accepts binary data as input, processes it according to instructions stored in its memory, and provides results as output. Microprocessors contain both combinational logic and sequential digital logic, and operate on numbers and symbols represented in the binary number system.

A microcontroller or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of NOR flash, OTP ROM, or ferroelectric RAM is also often included on the chip, as well as a small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general-purpose applications consisting of various discrete chips.

The Zilog Z80 is an 8-bit microprocessor designed by Zilog that played an important role in the evolution of early computing. Launched in 1976 and software-compatible with the Intel 8080, it offered a compelling alternative due to its better integration and increased performance. As well as the 8080's seven registers and flags register, the Z80 had an alternate register set that duplicated them, two 16-bit index registers and additional instructions including bit manipulation and block copy/search.

Zilog, Inc. is an American manufacturer of microprocessors, microcontrollers, and application-specific embedded system-on-chip (SoC) products.

The Intel 8008 is an early 8-bit microprocessor capable of addressing 16 KB of memory, introduced in April 1972. The 8008 architecture was designed by Computer Terminal Corporation (CTC) and was implemented and manufactured by Intel. While the 8008 was originally designed for use in CTC's Datapoint 2200 programmable terminal, an agreement between CTC and Intel permitted Intel to market the chip to other customers after Seiko expressed an interest in using it for a calculator.

The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. Sold for US$60, it was the first commercially produced microprocessor, and the first in a long line of Intel CPUs.

Atmel Corporation was a creator and manufacturer of semiconductors before being subsumed by Microchip Technology in 2016. Atmel was founded in 1984. The company focused on embedded systems built around microcontrollers. Its products included microcontrollers radio-frequency (RF) devices including Wi-Fi, EEPROM, and flash memory devices, symmetric and asymmetric security chips, touch sensors and controllers, and application-specific products. Atmel supplies its devices as standard products, application-specific integrated circuits (ASICs), or application-specific standard product (ASSPs) depending on the requirements of its customers.

Federico Faggin is an Italian-American physicist, engineer, inventor and entrepreneur. He is best known for designing the first commercial microprocessor, the Intel 4004. He led the 4004 (MCS-4) project and the design group during the first five years of Intel's microprocessor effort. Faggin also created, while working at Fairchild Semiconductor in 1968, the self-aligned MOS (metal–oxide–semiconductor) silicon-gate technology (SGT), which made possible MOS semiconductor memory chips, CCD image sensors, and the microprocessor. After the 4004, he led development of the Intel 8008 and 8080, using his SGT methodology for random logic chip design, which was essential to the creation of early Intel microprocessors. He was co-founder and CEO of Zilog, the first company solely dedicated to microprocessors, and led the development of the Zilog Z80 and Z8 processors. He was later the co-founder and CEO of Cygnet Technologies, and then Synaptics.

Masatoshi Shima is a Japanese electronics engineer. He was one of the architects of the world's first microprocessor, the Intel 4004. In 1968, Shima worked for Busicom in Japan, and did the logic design for a specialized CPU to be translated into three-chip custom chips. In 1969, he worked with Intel's Ted Hoff and Stanley Mazor to reduce the three-chip Busicom proposal into a one-chip architecture. In 1970, that architecture was transformed into a silicon chip, the Intel 4004, by Federico Faggin, with Shima's assistance in logic design.

V850 is a 32-bit RISC CPU architecture produced by Renesas Electronics for embedded microcontrollers. It was designed by NEC as a replacement for their earlier NEC V60 family, and was introduced shortly before NEC sold their designs to Renesas in the early 1990s. It has continued to be developed by Renesas as of 2018.

Bit slicing is a technique for constructing a processor from modules of processors of smaller bit width, for the purpose of increasing the word length; in theory to make an arbitrary n-bit central processing unit (CPU). Each of these component modules processes one bit field or "slice" of an operand. The grouped processing components would then have the capability to process the chosen full word-length of a given software design.

The history of general-purpose CPUs is a continuation of the earlier history of computing hardware.

In computer architecture, 12-bit integers, memory addresses, or other data units are those that are 12 bits wide. Also, 12-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, address buses, or data buses of that size.

Consumer IR, consumer infrared, or CIR is a class of devices employing the infrared portion of the electromagnetic spectrum for wireless communications. CIR ports are commonly found in consumer electronics devices such as television remote controls, PDAs, laptops, computers, and video game controllers.

PMOS or pMOS logic is a family of digital circuits based on p-channel, enhancement mode metal–oxide–semiconductor field-effect transistors (MOSFETs). In the late 1960s and early 1970s, PMOS logic was the dominant semiconductor technology for large-scale integrated circuits before being superseded by NMOS and CMOS devices.

In computer architecture, 16-bit integers, memory addresses, or other data units are those that are 16 bits wide. Also, 16-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, address buses, or data buses of that size. 16-bit microcomputers are microcomputers that use 16-bit microprocessors.

The NEC μCOM series is a series of microprocessors and microcontrollers manufactured by NEC in the 1970s and 1980s. The initial entries in the series were custom-designed 4 and 16-bit designs, but later models in the series were mostly based on the Intel 8080 and Zilog Z80 8-bit designs, and later, the Intel 8086 16-bit design. Most of the line was replaced in 1984 by the NEC V20, an Intel 8088 clone.

The COP400 or COP II is a 4-bit microcontroller family introduced in 1977 by National Semiconductor as a follow-on product to their original PMOS COP microcontroller. COP400 family members are complete microcomputers containing internal timing, logic, ROM, RAM, and I/O necessary to implement dedicated controllers. Some COP400 devices were second-sourced by Western Digital as the WD4200 family. In the Soviet Union several COP400 microcontrollers were manufactured as the 1820 series.

References

External links

• Saturn CPU
• "Products: High Performance 4-bit Microcontrollers (S1C63 family)". Epson. Archived from the original on 2013-07-29.
• Considerations for 4-bit processing