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.
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.
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.
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.
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.
|8020||1K × 8 ROM||64 × 8 RAM||subset of 8048, 20 pins, only 13 I/O lines|
|8021||1K × 8 ROM||64 × 8 RAM||subset of 8048, 28 pins, 21 I/O lines|
|8022||2K × 8 ROM||64 × 8 RAM||subset of 8048, A/D-converter|
|8035||none||64 × 8 RAM|
|8039||none||128 × 8 RAM|
|8040||none||256 × 8 RAM|
|8048||1K × 8 ROM||64 × 8 RAM|
|8049||2K × 8 ROM||128 × 8 RAM|
|8050||4K x 8 ROM||256 × 8 RAM|
|8748||1K × 8 EPROM||64 × 8 RAM|
|8749||2K × 8 EPROM||128 × 8 RAM|
|87P50||ext. ROM socket||256 × 8 RAM||Has piggy-back socket for 2758/2716/2732 EPROM.|
|8648||1K × 8 OTP EPROM||64 × 8 RAM||factory OTP EPROM|
|8041||1K × 8 ROM||64 × 8 RAM||Universal Peripheral Interface (UPI)|
|8041AH||1K × 8 ROM||128 × 8 RAM||UPI|
|8741A||1K × 8 EPROM||64 × 8 RAM||UPI, EPROM version of 8041|
|8741AH||1K × 8 OTP EPROM||128 × 8 RAM||UPI, OTP EPROM version of 8041AH|
|8042AH||2K × 8 ROM||256 × 8 RAM||UPI|
|8742||2K × 8 EPROM||128 × 8 RAM||UPI, EPROM version|
|8742AH||2K × 8 OTP EPROM||256 × 8 RAM||UPI, OTP EPROM version of 8042AH|
The Tandy/Radio Shack TRS-80 Model II, released in 1979, used the 8021 in its keyboard. 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.
The original IBM PC keyboard used an 8048 as its internal microcontroller. 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. 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.
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).
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.
- MCS-48 Single Component Microcomputer, Applications Seminar Notebook, 1978, Intel Corporation.
- MCS-48 MICROCOMPUTER USER'S MANUAL, 1978, Intel Corporation.
- Lionel Smith, Cecil Moore: Serial I/O and Math Utilities for the 8049 Microcomputer, Application Note AP-49, January 1979, Intel Corporation.
- A High-Speed Emulator for Intel MCS-48 Microcomputers, Application Note AP-55A, August 1979, Intel Corporation.
- Phil Dahm, Stuart Rosenberg: Intel MCS-48 and UPI-41A Microcontrollers, Reliability Report RR-25, December 1979, Intel Corporation.
- Microcontroller Handbook, Intel 1984, Order number 210918-002.
- 8-Bit Embedded Controllers, Intel 1991, Order number 270645-003.
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- Microprocessor Peripherals UPI-41A/41AH/42/42AH User's Manual, October 1993, Order number 231318-006, Intel Corporation.
- Johan Beaston, Jim Kahn: An 8741A/8041A Digital Cassette Controller, Application Note AP-90, May 1980, Intel Corporation.
- MCS-48 family architecture
- Coprolite 8048 Projects at the Wayback Machine (archived 17 July 2014)
- Computer History Museum, Intel 8048 Microcontroller Oral History Panel
- Microcontroller NEC 8741 (image of the Silicium-Chip)
- TRS-80 Model II Technical Reference Manual. Radio Shack. p. 135.
- Tandy 6000/6000HD Service Manual. Tandy/Radio Shack. 1985. p. 213.
- "Section 4: Keyboard", Technical Reference: Personal Computer, Personal Computer Hardware Reference Library (Revised ed.), IBM, April 1984
- "Section 1: System Board", Technical Reference: Personal Computer AT, Personal Computer Hardware Reference Library, IBM, September 1985
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- Datasheet (pdf) Philips MAB8400-Family