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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.
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 By the 1990s, most such uses had been replaced by general purpose binary designs.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
![](https://upload.wikimedia.org/wikipedia/commons/thumb/9/99/Alps_remote_control_BHR970001B_-_NEC_D63GS-7525.jpg/220px-Alps_remote_control_BHR970001B_-_NEC_D63GS-7525.jpg)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Intel_C4004_greytraces_CPU.jpg/220px-Intel_C4004_greytraces_CPU.jpg)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/Olympia_CD700_Desktop_Calculator._1971.Microprogrammable_Arithmetic_Processor_System_Devices_%28MAPS%29.jpg/220px-Olympia_CD700_Desktop_Calculator._1971.Microprogrammable_Arithmetic_Processor_System_Devices_%28MAPS%29.jpg)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Alps_remote_control_BHR970001B-7517.jpg/220px-Alps_remote_control_BHR970001B-7517.jpg)
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]
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
![](https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/National_Semiconductor_MM5700CA_D_Microprocessor.jpg/170px-National_Semiconductor_MM5700CA_D_Microprocessor.jpg)
- 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[23][24] (discontinued because of Low demand. "Last ship date: 7 March 2015"[25])
- 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][26] and μPD1724x[27] infrared remote control transmitter microcontrollers[28][29]
- EM Microelectronic-Marin EM6600 family,[30] EM6580,[31][32] EM6682,[33] etc.
- Epson S1C63 family
- National Semiconductor "COPS I" and "COPS II" ("COP400") 4-bit microcontroller families[34]
- National Semiconductor MAPS MM570X
- Sharp SM590/SM591/SM595[35]: 26–34
- Sharp SM550/SM551/SM552[35]: 36–48
- Sharp SM578/SM579[35]: 49–64
- Sharp SM5E4[35]: 65–74
- Sharp LU5E4POP[35]: 75–82
- Sharp SM5J5/SM5J6[35]: 83–99
- Sharp SM530[35]: 100–109
- Sharp SM531[35]: 110–118
- Sharp SM500[35]: 119–127 (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)
- Sharp SM5K1[35]: 128–140
- Sharp SM4A[35]: 141–148
- Sharp SM510[35]: 149–158 (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)
- Sharp SM511/SM512[35]: 159–171 (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)
- Sharp SM563[35]: 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
References
- ^ a b Ken Shirriff. "Reverse engineering RAM storage in early Texas Instruments calculator chips".
- ^ Mack, Pamela E. (2005-11-30). "The Microcomputer Revolution". Retrieved 2009-12-23.
- ^ "History in the Computing Curriculum" (PDF). Archived from the original (PDF) on 2011-07-19. Retrieved 2017-06-22.
- ^ TMS 1000 Series Data Manual (PDF). Texas Instruments. December 1976. Retrieved 2013-07-20.
- ^ "Rockwell PPS-4".
- ^ "Forth Chips". www.ultratechnology.com.
- ^ ISO/IEC 9899:1999 specification. p. 20, § 5.2.4.2.1. Retrieved 2023-07-24.
- ^ ISO/IEC 9899:1999 specification. p. 37, § 6.2.6.1 (4). Retrieved 2023-07-24.
- ^ Cline, Marshall. "C++ FAQ: the rules about bytes, chars, and characters".
- ^ "4-bit integer". cplusplus.com. Retrieved 2014-11-21.
- ^ Shima, Masatoshi; Faggin, Federico; Ungermann, Ralph; Slater, Michael (2007-04-27). "Zilog Oral History Panel on the Founding of the Company and the Development of the Z80 Microprocessor" (PDF).
- ^ Shirriff, Ken. "The Z-80 has a 4-bit ALU".
- ^ Hendrie, Gardner (2002-11-22). "Oral History of Edson (Ed) D. de Castro" (PDF) (Interview). p. 44.
- ^ "Nova 1200"
- ^ "The Saturn Processor". Retrieved 2015-12-23.
- ^ "Guide to the Saturn Processor". Retrieved 2014-01-14.
- ^ "Introduction to Saturn Assembly Language". Retrieved 2014-01-14.
- ^ "Desk Electronic Calculators: Casio AL-1000"
- ^ "Cateye Commuter Manual" (PDF). Retrieved 2014-02-11.
- ^ a b "μPD67, 67A, 68, 68A, 69 4-bit single-chip microcontroller for infrared remote control transmission" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2016-01-06.
- ^ Haskell, Richard. "Introduction to Digital Logic and Microprocessors (Lecture 12.2)". Archived from the original on 2014-02-22. Retrieved 2014-02-11.
- ^ Paul Reuvers and Marc Simons. Crypto Museum. "Barbie Typewriter", 2015
- ^ "MARC4 4-bit Microcontrollers – Programmer's Guide" (PDF). Atmel. Archived from the original (PDF) on 2014-12-15. Retrieved 2014-01-14.
- ^ "MARC4 4-Bit Architecture". Atmel. Archived from the original on 2009-05-31.
- ^ "Product End-of-Life (EOL) Notification" (PDF). Atmel. 2014-03-07. Archived from the original (PDF) on 2016-08-07.
- ^ "μPD6P9 4-bit single-chip microcontroller for infrared remote control transmission" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2016-03-27.
- ^ "μPD17240, 17241, 17242, 17243, 17244, 17245, 17246 4-bit single-chip microcontrollers for small general-purpose infrared remote control transmitters" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2016-03-27.
- ^ "Microcontrollers for Remote Controllers" (PDF). documentation.renesas.com. Archived from the original (PDF) on 2013-12-19.
- ^ "Mask ROM/ROMless Products 4/8bit Remote Control". Archived from the original on 2008-10-28.
- ^ Cravotta, Robert. "Embedded Processing Directory".
- ^ "EM6580". Archived from the original on 2013-12-19. Retrieved 2013-05-12.
- ^ "EM6580".
- ^ "EM6682".
- ^ Culver, John (2014-09-27). "National Semiconductor: The COP before the COPS". www.cpushack.com. Retrieved 2020-05-28.
- ^ a b c d e f g h i j k l m n Sharp Microcomputers Data Book (PDF). September 1990. Retrieved 2018-01-05.
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