Intel MCS-48

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Intel 8048 microcontroller KL Intel P8048H.jpg
Intel 8048 microcontroller
The 8749 with UV EPROM KL Intel D8749.jpg
The 8749 with UV EPROM
USSR KM1816BE48, an Intel 8748 clone KL USSR KM1816BE i8748 Black Background.jpg
USSR KM1816BE48, an Intel 8748 clone
An Intel 8049 microcontroller, as used in a HP3478A multimeter. This chip was manufactured in the second week of 1984. Intel 8049 Microcontroller.jpg
An Intel 8049 microcontroller, as used in a HP3478A multimeter. This chip was manufactured in the second week of 1984.

The MCS-48 microcontroller (µC) series, Intel's first microcontroller, was originally released in 1976. Its first members were 8048, 8035 and 8748. Initially this family was produced using NMOS technology, in the early 1980s it became available in CMOS technology. It was still manufactured into the 1990s to support older designs that still used it.

Microcontroller small computer on a single integrated circuit

A microcontroller is a small computer on a single integrated circuit. In modern terminology, it is similar to, but less sophisticated than, a system on a chip (SoC); an SoC may include a microcontroller as one of its components. A microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of ferroelectric RAM, NOR flash or OTP ROM is also often included on 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.

Intel American semiconductor company

Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, in the Silicon Valley. It is the world's second largest and second highest valued semiconductor chip manufacturer based on revenue after being overtaken by Samsung, and is the inventor of the x86 series of microprocessors, the processors found in most personal computers (PCs). Intel ranked No. 46 in the 2018 Fortune 500 list of the largest United States corporations by total revenue.

NMOS logic implements logic gates and other digital circuits

N-type metal-oxide-semiconductor logic uses n-type field-effect transistors (MOSFETs) to implement logic gates and other digital circuits. These nMOS transistors operate by creating an inversion layer in a p-type transistor body. This inversion layer, called the n-channel, can conduct electrons between n-type "source" and "drain" terminals. The n-channel is created by applying voltage to the third terminal, called the gate. Like other MOSFETs, nMOS transistors have four modes of operation: cut-off, triode, saturation, and velocity saturation.


The MCS-48 series has a modified Harvard architecture, with internal or external program ROM and 64–256 bytes of internal (on-chip) RAM. The I/O is mapped into its own address space, separate from programs and data. The 8048 is probably the most prominent member of Intel's MCS-48 family of microcontrollers.

The modified Harvard architecture is a variation of the Harvard computer architecture that allows the contents of the instruction memory to be accessed as if it were data. Most modern computers that are documented as Harvard architecture are, in fact, modified Harvard architecture.

Read-only memory non-volatile memory used in computers and other electronic devices; class of storage medium used in computers and other electronic devices

Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to store firmware or application software in plug-in cartridges.

Random-access memory form of computer data storage

Random-access memory is a form of computer data storage that stores data and machine code currently being used. A random-access memory device allows data items to be read or written in almost the same amount of time irrespective of the physical location of data inside the memory. In contrast, with other direct-access data storage media such as hard disks, CD-RWs, DVD-RWs and the older magnetic tapes and drum memory, the time required to read and write data items varies significantly depending on their physical locations on the recording medium, due to mechanical limitations such as media rotation speeds and arm movement.

Though the MCS-48 series was eventually replaced by the very popular MCS-51 series, even at around year 2000 it remained quite popular, due to its low cost, wide availability, memory-efficient one-byte instruction set, and mature development tools. Because of this, it is much used in high-volume consumer electronics devices such as TV sets, TV remotes, toys, and other gadgets where cost cutting is essential.

Intel MCS-51 microcontroller chip

The Intel MCS-51 is a single chip microcontroller (MCU) series developed by Intel in 1980 for use in embedded systems. The architect of the instruction set of the Intel MCS-51 was John H. Wharton. Intel's original versions were popular in the 1980s and early 1990s and enhanced binary compatible derivatives remain popular today. It is an example of a complex instruction set computer, and has separate memory spaces for program instructions and data.


The 8049 has 2 KB of masked ROM (the 8748 and 8749 had EPROM) that can be replaced with a 4 KB external ROM, as well as 128  bytes of RAM and 27  I/O ports. The µC's oscillator block divides the incoming clock into 15 internal phases, thus with its 11  MHz max. crystal one gets 0.73  MIPS (of one-clock instructions). Some 70% of instructions are single byte/cycle ones, but 30% need two cycles and/or two bytes, so the raw performance would be closer to 0.5 MIPS.

An EPROM, or erasable programmable read-only memory, is a type of memory chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored data after a power supply has been turned off and back on is called non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages than those normally used in digital circuits. Once programmed, an EPROM can be erased by exposing it to strong ultraviolet light source. EPROMs are easily recognizable by the transparent fused quartz window in the top of the package, through which the silicon chip is visible, and which permits exposure to ultraviolet light during erasing.

The byte is a unit of digital information that most commonly consists of eight bits, representing a binary number. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit of memory in many computer architectures.

In computing, input/output or I/O is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals or data received by the system and outputs are the signals or data sent from it. The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation.

The Intel 8748 has on-chip clock oscillator, 2× 8-bit timers, 27× I/O ports, 64 bytes of RAM and 1 KB of EPROM. A version with 2 KB EPROM and 128 bytes RAM was also available under the 8749 number.

80201K × 8 ROM64 × 8 RAMsubset of 8048, 20 pins, only 13 I/O lines
80211K × 8 ROM64 × 8 RAMsubset of 8048, 28 pins, 21 I/O lines
80222K × 8 ROM64 × 8 RAMsubset of 8048, A/D-converter
8035none64 × 8 RAM
8039none128 × 8 RAM
8040none256 × 8 RAM
80481K × 8 ROM64 × 8 RAM
80492K × 8 ROM128 × 8 RAM
80504K x 8 ROM256 × 8 RAM
87481K × 8 EPROM64 × 8 RAM
87492K × 8 EPROM128 × 8 RAM
87P50ext. ROM socket256 × 8 RAMHas piggy-back socket for 2758/2716/2732 EPROM.
86481K × 8 OTP EPROM64 × 8 RAMfactory OTP EPROM

80411K × 8 ROM64 × 8 RAMUniversal Peripheral Interface (UPI)
8041AH1K × 8 ROM128 × 8 RAMUPI
8741A1K × 8 EPROM64 × 8 RAMUPI, EPROM version of 8041
8741AH1K × 8 OTP EPROM128 × 8 RAMUPI, OTP EPROM version of 8041AH
8042AH2K × 8 ROM256 × 8 RAMUPI
87422K × 8 EPROM128 × 8 RAMUPI, EPROM version
8742AH2K × 8 OTP EPROM256 × 8 RAMUPI, OTP EPROM version of 8042AH


The Tandy/Radio Shack TRS-80 Model II, released in 1979, used the 8021 in its keyboard. [1] The 8021 allowed the Model II to be the first desktop computer system with a separate detachable lightweight keyboard connected with by a single thin flexible wire, and likely the first keyboard to use a dedicated microprocessor, both attributes that would later be copied years later by Apple and IBM. The 8021 processor scans the key matrix, converts switch closures to an 8-bit code and then transmits that code serially to the keyboard interface on the main system. The 8021 will also accept commands to turn indicator LEDs on or off. This was all done with just four chips, a remarkable feat at the time. The 8021 was also used in the keyboards for the TRS-80 Model 12, 12B, 16, 16B and the Tandy 6000/6000HD. [2]

TRS-80 Model II

The TRS-80 Model II was a computer system launched by Tandy in October 1979, and targeted at the small-business market.

The original IBM PC keyboard used an 8048 as its internal microcontroller. [3] The PC AT replaced the PC's Intel 8255 peripheral interface chip at I/O port addresses 0x60–63 with an 8042 accessible through port addresses 0x60 and 0x64. [4] As well as managing the keyboard interface, the 8042 controlled the A20 line gating function for the AT's Intel 80286 CPU and could be commanded by software to reset the 80286 (unlike the 80386 and later processors, the 80286 had no way of switching from protected mode back to real mode except by being reset). Later PC compatibles integrate the 8042's functions into their super I/O devices.

The keyboard for IBM PC-compatible computers is standardized. However, during the more than 30 years of PC architecture being frequently updated, many keyboard layout variations have been developed.

IBM Personal Computer/AT

The IBM Personal Computer AT, more commonly known as the IBM AT and also sometimes called the PC AT or PC/AT, was IBM's second-generation PC, designed around the 6 MHz Intel 80286 microprocessor and released in 1984 as System Unit 5170. The name AT stood for "Advanced Technology," and was chosen because the AT offered various technologies that were then new in personal computers; one such advancement was that the 80286 processor supported protected mode. IBM later released an 8 MHz version of the AT.

Intel 8255

The Intel 8255 Programmable Peripheral Interface (PPI) chip was developed and manufactured by Intel in the first half of the 1970s for the Intel 8080 microprocessor. The 8255 provides 24 parallel input/output lines with a variety of programmable operating modes.

The 8048 was used in the Magnavox Odyssey² video game console, the Korg Trident series, [5] the Korg Poly-61, [6] Roland Jupiter-4 and Roland ProMars [7] analog synthesizers.

Philips Semiconductors (now NXP) owned a license to produce this series and developed their MAB8400-family based on this architecture. These were the first microcontrollers with an integrated I²C-interface and were used in the first Philips (Magnavox in the US) Compact Disc players (e.g. the CD-100). [8]

Another variant, the ROM-less 8035, was used in Nintendo's arcade game Donkey Kong . Although not being a typical application for a microcontroller, its purpose was to generate the background music of the game.



See also

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In computer architecture, 16-bit integers, memory addresses, or other data units are those that are 16 bits wide. Also, 16-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 16-bit microcomputers are computers in which 16-bit microprocessors were the norm.

Single-board microcontroller

A single-board microcontroller is a microcontroller built onto a single printed circuit board. This board provides all of the circuitry necessary for a useful control task: a microprocessor, I/O circuits, a clock generator, RAM, stored program memory and any necessary support ICs. As such, they are a kind of System on a Chip (SoC). The intention is that the board is immediately useful to an application developer, without requiring them to spend time and effort to develop controller hardware.

Keyboard controller (computing)

In computing, a keyboard controller is a device that interfaces a keyboard to a computer. Its main function is to inform the computer when a key is pressed or released. When data from the keyboard arrives, the controller raises an interrupt to allow the CPU to handle the input.


  1. TRS-80 Model II Technical Reference Manual. Radio Shack. p. 135.
  2. Tandy 6000/6000HD Service Manual. Tandy/Radio Shack. 1985. p. 213.
  3. "Section 4: Keyboard", Technical Reference: Personal Computer, Personal Computer Hardware Reference Library (Revised ed.), IBM, April 1984
  4. "Section 1: System Board", Technical Reference: Personal Computer AT, Personal Computer Hardware Reference Library, IBM, September 1985
  5. "Korg Trident Service Manual". Korg. p. 4. Retrieved 10 February 2018 via Synthfool.
  6. "Korg Poly-61 Service Manual" (PDF).
  7. Gordon Reid (November 2004). "The History Of Roland, Part 1: 1930–1978". The History Of Roland. Sound On Sound Magazine. Retrieved 29 November 2010.
  8. Datasheet (pdf) Philips MAB8400-Family

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.