Intel 8051
Encyclopedia
Harvard architecture
The Harvard architecture is a computer architecture with physically separate storage and signal pathways for instructions and data. The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape and data in electro-mechanical counters...
, single chip microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
(µC) series which was developed by Intel in 1980 for use in embedded system
Embedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
s. Intel's original versions were popular in the 1980s and early 1990s. While Intel no longer manufactures the MCS-51, binary compatible derivatives remain popular today. In addition to these physical devices, several companies also offer MCS-51 derivatives as IP cores for use in FPGAs or ASICs
ASICS
ASICS is a Japanese athletic equipment company. ASICS produces professional footwear and sports equipment designed for football, running, netball, tennis, badminton, squash, martial arts, cricket, golf, wrestling, track & field, cross-training, volleyball, cheerleading, lacrosse, and for many other...
designs.
Intel's original MCS-51 family was developed using NMOS
NMOS logic
N-type metal-oxide-semiconductor logic uses n-type metal-oxide-semiconductor field effect transistors to implement logic gates and other digital circuits...
technology, but later versions, identified by a letter C in their name (e.g., 80C51) used CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
technology and consumed less power than their NMOS predecessors. This made them more suitable for battery-powered devices.
Important features and applications
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, RAM, ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
, I/O
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , 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...
, interrupt
Interrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
logic, timer
Timer
A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass.Timers can be mechanical, electromechanical,...
, etc.) in a single package
Integrated circuit packaging
Integrated circuit packaging is the final stage of semiconductor device fabrication per se, followed by IC testing.Packaging in ceramic or plastic prevents physical damage and corrosion and supports the electrical contacts required to assemble the integrated circuit into a system.In the integrated...
- 8-bit ALUArithmetic logic unitIn computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations.The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
, Accumulator and 8-bit Registers; hence it is an 8-bit8-bitThe first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
microcontrollerMicrocontrollerA microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM... - 8-bit data bus – It can access 8 bits of data in one operation
- 16-bit address busAddress busAn address bus is a computer bus that is used to specify a physical address. When a processor or DMA-enabled device needs to read or write to a memory location, it specifies that memory location on the address bus...
– It can access 216 memory locations – 64 KBKilobyteThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
(65536 locations) each of RAM and ROM - On-chip RAM – 128 bytes (data memory)
- On-chip ROM – 4 kByte (program memory)
- Four byteByteThe byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
bi-directional input/outputInput/outputIn computing, input/output, or I/O, refers to the communication between an information processing system , 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...
port - UART (serial portSerial portIn computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
) - Two 16-bit Counter/timerTimerA timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass.Timers can be mechanical, electromechanical,...
s - Two-level interruptInterruptIn computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
priority - Power savingPower managementPower management is a feature of some electrical appliances, especially copiers, computers and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power state when inactive. In computing this is known as PC power management and is built...
mode (on some derivatives)
One particularly useful feature of the 8051 core was the inclusion of a boolean
Boolean datatype
In computer science, the Boolean or logical data type is a data type, having two values , intended to represent the truth values of logic and Boolean algebra...
processing engine which allows bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
-level boolean logic
Boolean logic
Boolean algebra is a logical calculus of truth values, developed by George Boole in the 1840s. It resembles the algebra of real numbers, but with the numeric operations of multiplication xy, addition x + y, and negation −x replaced by the respective logical operations of...
operations to be carried out directly and efficiently on select internal registers and select RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
locations. This advantageous feature helped cement the 8051's popularity in industrial control applications because it reduced code size by as much as 30%. Another valued feature is the including of four bank selectable
Bank switching
Bank switching is a technique to increase the amount of usable memory beyond the amount directly addressable by the processor. It can be used to configure a system differently at different times; for example, a ROM required to start a system from diskette could be switched out when no longer...
working register sets which greatly reduce the amount of time required to complete an interrupt service routine
Interrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
. With a single instruction the 8051 can switch register banks as opposed to the time consuming task of transferring the critical registers to the stack or designated RAM locations. These registers also allowed the 8051 to quickly perform a context switch
Context switch
A context switch is the computing process of storing and restoring the state of a CPU so that execution can be resumed from the same point at a later time. This enables multiple processes to share a single CPU. The context switch is an essential feature of a multitasking operating system...
which is essential for time sensitive real-time
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
applications.
The MCS-51 UARTs make it simple to use the chip as a serial communications interface. External pins can be configured to connect to internal shift registers in a variety of ways, and the internal timers can also be used, allowing serial communications in a number of modes, both synchronous and asynchronous. Some modes allow communications with no external components. A mode compatible with an RS-485 multi-point communications environment is achievable, but the 8051's real strength is fitting in with existing ad-hoc protocols (e.g., when controlling serial-controlled devices).
Once a UART, and a timer if necessary, have been configured, the programmer needs only to write a simple interrupt routine to refill the send shift register whenever the last bit is shifted out by the UART and/or empty the full receive shift register (copy the data somewhere else). The main program then performs serial reads and writes simply by reading and writing 8-bit data to stacks.
MCS-51 based microcontrollers typically include one or two UARTs, two or three timers, 128 or 256 bytes of internal data RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
(16 bytes of which are bit-addressable), up to 128 bytes of I/O
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , 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...
, 512 bytes to 64 kB of internal program memory, and sometimes a quantity of extended data RAM (ERAM) located in the external data space. The original 8051 core ran at 12 clock cycles per machine cycle, with most instructions executing in one or two machine cycles. With a 12 MHz clock frequency, the 8051 could thus execute 1 million one-cycle instructions per second or 500,000 two-cycle instructions per second. Enhanced 8051 cores are now commonly used which run at six, four, two, or even one clock per machine cycle, and have clock frequencies of up to 100 MHz, and are thus capable of an even greater number of instructions per second. All SILabs, some Dallas and a few Atmel devices have single cycle cores.
Features of the modern 8051 include built-in reset timers with brown-out detection, on-chip oscillators, self-programmable Flash ROM program memory, bootloader code in ROM, EEPROM non-volatile data storage, I²C
I²C
I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...
, SPI, and USB host interfaces, CAN or LIN
Local Interconnect Network
The LIN-Bus is a vehicle bus standard or computer networking bus-system used within current automotive network architectures....
bus, PWM
Pulse-width modulation
Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....
generators, analog comparators, A/D and D/A converters, RTC
Real-time clock
A real-time clock is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.-Terminology:The term is used to avoid...
s, extra counters and timers, in-circuit debugging facilities, more interrupt sources, and extra power saving modes.
In many engineering schools the 8051 microcontroller is used in introductory microcontroller courses.
Memory architecture
The MCS-51 has four distinct types of memory – internal RAM, special function registers, program memory, and external data memory.Internal RAM
Internal RAM
Internal RAM, or IRAM, is the address range of RAM that is internal to the CPU. Some object files contain an .iram section.Generally, IRAM is composed of very high speed SRAM located alongside of the CPU. It acts similar to a cache, but is software addressable...
(IRAM) is located from address 0 to address 0xFF. IRAM from 0x00 to 0x7F can be accessed directly, and the bytes from 0x20 to 0x2F are also bit-addressable. IRAM from 0x80 to 0xFF must be accessed indirectly, using the @R0 or @R1 syntax, with the address to access loaded in R0 or R1.
Special function registers (SFR) are located from address 0x80 to 0xFF, and are accessed directly using the same instructions as for the lower half of IRAM. Some of the SFR's are also bit-addressable.
Program memory (PMEM, though less common in usage than IRAM and XRAM) is located starting at address 0. It may be on- or off-chip, depending on the particular model of chip being used. Program memory is read-only, though some variants of the 8051 use on-chip flash memory and provide a method of re-programming the memory in-system or in-application. Aside from storing code, program memory can also store tables of constants that can be accessed by MOVC A, @DPTR, using the 16-bit special function register DPTR.
External data memory (XRAM) also starts at address 0. It can also be on- or off-chip; what makes it "external" is that it must be accessed using the MOVX (Move eXternal) instruction. Many variants of the 8051 include the standard 256 bytes of IRAM plus a few KB of XRAM on the chip. If more XRAM is required by an application, the internal XRAM can be disabled, and all MOVX instructions will fetch from the external bus.
Programming
There are various high-level programming languageHigh-level programming language
A high-level programming language is a programming language with strong abstraction from the details of the computer. In comparison to low-level programming languages, it may use natural language elements, be easier to use, or be from the specification of the program, making the process of...
compilers for the 8051
8051 compiler
There are various high level language compilers for 8051 or enhanced versions of 8051 from various vendors. The most popular is the C language compiler. As the modern C compilers are efficient, assembly language is seldom used nowadays. It is common to have a complete program written solely in C...
. Several C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
compilers are available for the 8051, most of which feature extensions that allow the programmer to specify where each variable should be stored in its six types of memory, and provide access to 8051 specific hardware features such as the multiple register banks and bit manipulation instructions. There are many commercial C compilers. SDCC
Small Device C Compiler
The Small Device C Compiler is an open source, partially retargetable C compiler for microcontrollers. It is distributed under the GNU General Public License. The package also contains a linker, assembler, simulator and debugger...
is a popular open source C compiler. Other high level languages such as Forth, BASIC, Pascal/Object Pascal
Object Pascal
Object Pascal refers to a branch of object-oriented derivatives of Pascal, mostly known as the primary programming language of Embarcadero Delphi.-Early history at Apple:...
, PL/M
PL/M
The PL/M programming languageis a high-level language developed byGary Kildall in 1972 for Intel for its microprocessors....
and Modula-2
Modula-2
Modula-2 is a computer programming language designed and developed between 1977 and 1980 by Niklaus Wirth at ETH Zurich as a revision of Pascal to serve as the sole programming language for the operating system and application software for the personal workstation Lilith...
are available for the 8051, but they are less widely used than C and assembly
Assembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
.
Because IRAM, XRAM, and PMEM all have an address 0, C compilers for the 8051 architecture provide compiler-specific pragma
Directive (programming)
In computer programming, the term directive is applied in a variety of ways that are similar to the term command. It is also used to describe some programming language constructs ....
s or other extensions to indicate where a particular piece of data should be stored (i.e. constants in PMEM or variables needing fast access in IRAM). Since data could be in one of three memory spaces, a mechanism is usually provided to allow determining to which memory a pointer refers, either by constraining the pointer type to include the memory space, or by storing metadata with the pointer.
Instruction set
The MCS-51 instruction set offers several addressing modes, including- direct register, using ACC (the accumulator) and R0-R7
- direct memory, which access the internal RAM or the SFR's, depending on the address
- indirect memory, using R0, R1, or DPTR to hold the memory address. The instruction used may vary to access internal RAM, external RAM, or program memory.
- individual bits of a range of IRAM and some of the SFR's
Many of the operations allow any addressing mode for the source or the destination, for example, MOV 020h, 03fh will copy the value in memory location 0x3f in the internal RAM to the memory location 0x20, also in internal RAM.
Because the 8051 is an accumulator-based architecture, all arithmetic operations must use the accumulator, e.g. ADD A, 020h will add the value in memory location 0x20 in the internal RAM to the accumulator.
One does not need to master these instructions to program the 8051. With the availability of good quality C compilers, including open source SDCC
Small Device C Compiler
The Small Device C Compiler is an open source, partially retargetable C compiler for microcontrollers. It is distributed under the GNU General Public License. The package also contains a linker, assembler, simulator and debugger...
, virtually all programs can be written with high-level language.
Related processors
Intel MCS-48
The MCS-48 microcontroller series, Intel's first microcontroller, was originally released in 1976. Its first members were 8048, 8035 and 8748....
, was used in the keyboard of the first IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
, where it converted keypresses into the serial data stream which is sent to the main unit of the computer. The 8048 and derivatives are still used for basic model keyboards.
The 8031 was a cut down version of the original Intel 8051 that did not contain any internal program memory (ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
). To use this chip, external ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
had to be added containing the program that the 8031 would fetch and execute. An 8051 chip could be sold as a ROM-less 8031, as the 8051's internal ROM is disabled by the normal state of the EA pin in an 8031-based design. A vendor might sell an 8051 as an 8031 for any number of reasons, such as faulty code in the 8051's ROM, or simply an oversupply of 8051's and undersupply of 8031's.
The 8052 was an enhanced version of the original 8051 that featured 256 bytes of internal RAM instead of 128 bytes, 8 KB of ROM instead of 4 KB, and a third 16-bit timer. The 8032 had these same features except for the internal ROM program memory. The 8052 and 8032 are largely considered to be obsolete because these features and more are included in nearly all modern 8051 based microcontrollers.
Intel discontinued its MCS-51 product line in March 2007, however there are plenty of enhanced 8051 products or silicon intellectual property
Silicon intellectual property
Silicon Intellectual Property is a business model for a semiconductor company where the company licenses its technology to a customer as intellectual property. This is a type of fabless semiconductor company which doesn't provide physical chips to its customers but merely facilitates the...
added regularly from other vendors. Current vendors of MCS-51 compatible processors include more than 20 independent manufacturers including Atmel
Atmel
Atmel Corporation is a manufacturer of semiconductors, founded in 1984. Its focus is on system-level solutions built around flash microcontrollers...
, Infineon Technologies
Infineon Technologies
Infineon Technologies AG is a German semiconductor manufacturer and was founded on April 1, 1999, when the semiconductor operations of the parent company Siemens AG were spun off to form a separate legal entity. , Infineon has 25,149 employees worldwide...
(formerly Siemens AG
Siemens AG
Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....
), Maxim Integrated Products
Maxim Integrated Products
Maxim Integrated Products is a publicly traded company that designs, manufactures, and sells analog and mixed-signal semiconductor products. Maxim develops integrated circuits for the industrial, communications, consumer, and computing markets....
(via its Dallas Semiconductor
Dallas Semiconductor
Dallas Semiconductor, now a subsidiary of Maxim Integrated Products, designs and manufactures analog, digital, and mixed-signal semiconductors...
subsidiary), NXP (formerly Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
Semiconductor), Microchip Technology
Microchip Technology
Microchip Technology is an American manufacturer of microcontroller, memory and analog semiconductors. Its products include microcontrollers , Serial EEPROM devices, Serial SRAM devices, KEELOQ devices, radio frequency devices, thermal, power and battery management analog devices, as well as...
, Nuvoton (formerly Winbond
Winbond
Winbond Electronics Corporation is a Taiwan-based corporation founded in 1987 that produces semiconductors and several types of integrated circuits, most notably Dynamic RAM, Static RAM, microcontrollers, and personal computer ICs...
), ST Microelectronics, Silicon Laboratories
Silicon Laboratories
Silicon Laboratories, Inc. is a mixed signal fabless semiconductor company based in Austin, Texas.The company was founded in 1996 by three veterans from the former Crystal Semiconductor – Nav Sooch, Dave Welland and Jeff Scott . The company's CEO is Necip Sayiner. The company went public in...
(formerly Cygnal), Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
, Ramtron International
Ramtron International
Ramtron International Corporation , located in Colorado Springs, CO, is the main supplier of F-RAM chips and integrated semiconductor products. The company sells serial and parallel ferroelectric random access memory devices and Processor Companion devices that integrate a variety of common...
, Silicon Storage Technology
Silicon Storage Technology
Silicon Storage Technology, Inc. is a Sunnyvale, California, USA, technology company producing non-volatile memory devices and related products.It was founded by Bing Yeh in 1989....
, Cypress Semiconductor
Cypress Semiconductor
Cypress Semiconductor Corporation is a Silicon Valley-based semiconductor design and manufacturing company founded by T. J. Rodgers and others from Advanced Micro Devices. It was formed in 1982 with backing by Sevin Rosen and went public in 1986. The company initially focused on the design and...
and Analog Devices
Analog Devices
Analog Devices, Inc. , known as ADI, is an American multinational semiconductor company specializing in data conversion and signal conditioning technology, headquartered in Norwood, Massachusetts...
.
The 80C537 and 80C517 are CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
versions, designed for the automotive industry
Automotive industry
The automotive industry designs, develops, manufactures, markets, and sells motor vehicles, and is one of the world's most important economic sectors by revenue....
. Enhancements mostly new peripheral features and expanded arithmetic instructions. The 80C517 has fail save mechanisms, analog signal processing facilities and timer capabilities and 8 KB on-chip program memory. Other features include:
- 256 byte on-chip RAM
- 256 directly addressable bits
- External program and data memory expandable up to 64 KB
- 8-bit A/D converter with 12 multiplexed inputs
- Arithmetic unit can make division, multiplication, shift and normalize operations
- Eight data pointers instead of one for indirect addressing of program and external data memory
- Extended watchdog facilities
- Nine ports
- Two full-duplex serial interfaces with own baud rate generators
- Four priority level interrupt systems, 14 interrupt vectors
- Three power saving modes
Use as intellectual property
Today, 8051s are still available as discrete parts, but they are mostly used as silicon intellectual propertySilicon intellectual property
Silicon Intellectual Property is a business model for a semiconductor company where the company licenses its technology to a customer as intellectual property. This is a type of fabless semiconductor company which doesn't provide physical chips to its customers but merely facilitates the...
cores. Available in high-level language source code (VHDL or Verilog) or FPGA
Field-programmable gate array
A field-programmable gate array is an integrated circuit designed to be configured by the customer or designer after manufacturing—hence "field-programmable"...
netlist
Netlist
The word netlist can be used in several different contexts, but perhaps the most popular is in the field of electronic design. In this context, a "netlist" describes the connectivity of an electronic design....
forms, these cores are typically integrated within embedded systems, in products ranging from USB flash drive
USB flash drive
A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...
s to washing machines to complex wireless communication systems on a chip. Designers use 8051 silicon IP cores, because of the smaller size, and lower power, compared to 32 bit processors like ARM M series
ARM architecture
ARM is a 32-bit reduced instruction set computer instruction set architecture developed by ARM Holdings. It was named the Advanced RISC Machine, and before that, the Acorn RISC Machine. The ARM architecture is the most widely used 32-bit ISA in numbers produced...
, MIPS
MIPS architecture
MIPS is a reduced instruction set computer instruction set architecture developed by MIPS Technologies . The early MIPS architectures were 32-bit, and later versions were 64-bit...
and BA22.
Modern 8051 cores are faster than earlier packaged versions. Design improvements have increased 8051 performance while retaining compatibility with the original MCS 51 instruction set. The original Intel 8051 ran at 12 clock cycles per machine cycle, and most instructions executed in one or two machine cycles. A typical maximum clock frequency of 12 MHz meant these old 8051s could execute one million single-cycle instructions, or 500,000 two-cycle instructions, per second. In contrast, enhanced 8051 silicon IP cores now run at one clock cycle per machine cycle, and have clock frequencies of up to 450 MHz. That means an 8051-compatible processor can now execute 450 million instructions per second.
Literature
- MCS® 51 Microcontroller Family User's Manual, February 1994, Publication number 121517, Intel Corporation; PDF.
- MCS-51TM Macro Assembler User's Guide, Publication number 9800937, Intel Corporation.
- Microcontroller Handbook. Intel 1984, Order number 210918-002.
- 8-Bit Embedded Controllers. Intel 1991, Order number 270645-003.