Микроконтроллеры: Компьютеры на одной микросхеме

Small computer on a single integrated circuit
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A microcontroller (MC, UC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) 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 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. In modern terminology, a microcontroller is similar to, but less sophisticated than, a system on a chip (SoC). A SoC may include a microcontroller as one of its components, but usually integrates it with advanced peripherals like a graphics processing unit (GPU), a Wi Fi module, or one or more coprocessors. Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make digital control of more devices and processes practical. Mixed signal microcontrollers are common, integrating analog components needed to control non digital electronic systems. In the context of the internet of things, microcontrollers are an economical and popular means of data collection, sensing and actuating the physical world as edge devices. Some microcontrollers may use four bit words and operate at frequencies as low as 4 kHz for low power consumption (single digit milliwatts or microwatts). They generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting battery applications. Other microcontrollers may serve performance critical roles, where they may need to act more like a digital signal processor (DSP), with higher clock speeds and power consumption.

One book credits TI engineers Gary Boone and Michael Cochran with the successful creation of the first microcontroller in 1971. The result of their work was the TMS 1000, which became commercially available in 1974. It combined read only memory, read/write memory, processor and clock on one chip and was targeted at embedded systems. During the early to mid 1970s, Japanese electronics manufacturers began producing microcontrollers for automobiles, including 4 bit MCUs for in car entertainment, automatic wipers, electronic locks, and dashboard, and 8 bit MCUs for engine control. Partly in response to the existence of the single chip TMS 1000, Intel developed a computer system on a chip optimized for control applications, the Intel 8048, with commercial parts first shipping in 1977. to be electrically erased quickly without an expensive package as required for EPROM, allowing both rapid prototyping, and in system programming. (EEPROM technology had been available prior to this time, but the earlier EEPROM was more expensive and less durable, making it unsuitable for low cost mass produced microcontrollers.) The same year, Atmel introduced the first microcontroller using Flash memory, a special type of EEPROM. Other companies rapidly followed suit, with both memory types. Nowadays microcontrollers are cheap and readily available for hobbyists, with large online communities around certain processors.

In 2002, about 55% of all CPUs sold in the world were 8 bit microcontrollers and microprocessors. Over two billion 8 bit microcontrollers were sold in 1997, and according to Semico, over four billion 8 bit microcontrollers were sold in 2006. More recently, Semico has claimed the MCU market grew 36.5% in 2010 and 12% in 2011. A typical home in a developed country is likely to have only four general purpose microprocessors but around three dozen microcontrollers. A typical mid range automobile has about 30 microcontrollers. They can also be found in many electrical devices such as washing machines, microwave ovens, and telephones. Cost to manufacture can be under per unit. Cost has plummeted over time, with the cheapest 8 bit microcontrollers being available for under $0.03 in 2018, and some 32 bit microcontrollers around for similar quantities. In 2012, following a global crisis—a worst ever annual sales decline and recovery and average sales price year over year plunging 17%—the biggest reduction since the 1980s—the average price for a microcontroller was ( for 4 /8 bit, for 16 bit, for 32 bit). In 2015, 8 bit microcontrollers could be bought for (1,000 units), 16 bit for (1,000 units), and 32 bit for (1,000 units, but at for 5,000). In 2018, 8 bit microcontrollers could be bought for , and 32 bit for (1,000 units, but at for 5,000). In 2018, the low priced microcontrollers above from 2015 were all more expensive (with inflation calculated between 2018 and 2015 prices for those specific units) at: the 8 bit microcontroller could be bought for (1,000 units) or 2.6% higher, The device is 1/10th the size of IBM's previously claimed world record sized computer from months back in March 2018, which is "smaller than a grain of salt", has a million transistors, costs less than to manufacture, and, combined with blockchain technology, is intended for logistics and "crypto anchors"—digital fingerprint applications.

A microcontroller can be considered a self contained system with a processor, memory and peripherals and can be used as an embedded system. The majority of microcontrollers in use today are embedded in other machinery, such as automobiles, telephones, appliances, and peripherals for computer systems. While some embedded systems are very sophisticated, many have minimal requirements for memory and program length, with no operating system, and low software complexity. Typical input and output devices include switches, relays, solenoids, LED's, small or custom liquid crystal displays, radio frequency devices, and sensors for data such as temperature, humidity, light level etc. Embedded systems usually have no keyboard, screen, disks, printers, or other recognizable I/O devices of a personal computer, and may lack human interaction devices of any kind.

Microcontrollers must provide real time (predictable, though not necessarily fast) response to events in the embedded system they are controlling. When certain events occur, an interrupt system can signal the processor to suspend processing the current instruction sequence and to begin an interrupt service routine (ISR, or "interrupt handler") which will perform any processing required based on the source of the interrupt, before returning to the original instruction sequence. Possible interrupt sources are device dependent and often include events such as an internal timer overflow, completing an analog to digital conversion, a logic level change on an input such as from a button being pressed, and data received on a communication link. Where power consumption is important as in battery devices, interrupts may also wake a microcontroller from a low power sleep state where the processor is halted until required to do something by a peripheral event.

Typically microcontroller programs must fit in the available on chip memory, since it would be costly to provide a system with external, expandable memory. Compilers and assemblers are used to convert both high level and assembly language code into a compact machine code for storage in the microcontroller's memory. Depending on the device, the program memory may be permanent, read only memory that can only be programmed at the factory, or it may be field alterable flash or erasable read only memory. Manufacturers have often produced special versions of their microcontrollers in order to help the hardware and software development of the target system. Originally these included EPROM versions that have a "window" on the top of the device through which program memory can be erased by ultraviolet light, ready for reprogramming after a programming ("burn") and test cycle. Since 1998, EPROM versions are rare and have been replaced by EEPROM and flash, which are easier to use (can be erased electronically) and cheaper to manufacture. Other versions may be available where the ROM is accessed as an external device rather than as internal memory, however these are becoming rare due to the widespread availability of cheap microcontroller programmers. The use of field programmable devices on a micro controller may allow field update of the firmware or permit late factory revisions to products that have been assembled but not yet shipped. Programmable memory also reduces the lead time required for deployment of a new product. Where hundreds of thousands of identical devices are required, using parts programmed at the time of manufacture can be economical. These "mask programmed" parts have the program laid down in the same way as the logic of the chip, at the same time. A customized microcontroller incorporates a block of digital logic that can be personalized for additional processing capability, peripherals and interfaces that are adapted to the requirements of the application. One example is the AT91CAP from Atmel.

Microcontrollers usually contain from several to dozens of general purpose input/output pins (GPIO). GPIO pins are software configurable to either an input or an output state. When GPIO pins are configured to an input state, they are often used to read sensors or external signals. Configured to the output state, GPIO pins can drive external devices such as LEDs or motors, often indirectly, through external power electronics. Many embedded systems need to read sensors that produce analog signals. This is the purpose of the analog to digital converter (ADC). Since processors are built to interpret and process digital data, i. e. 1s and 0s, they are not able to do anything with the analog signals that may be sent to it by a device. So the analog to digital converter is used to convert the incoming data into a form that the processor can recognize. A less common feature on some microcontrollers is a digital to analog converter (DAC) that allows the processor to output analog signals or voltage levels. In addition to the converters, many embedded microprocessors include a variety of timers as well. One of the most common types of timers is the programmable interval timer (PIT). A PIT may either count down from some value to zero, or up to the capacity of the count register, overflowing to zero. Once it reaches zero, it sends an interrupt to the processor indicating that it has finished counting. This is useful for devices such as thermostats, which periodically test the temperature around them to see if they need to turn the air conditioner on/off, the heater on/off, etc. A dedicated pulse width modulation (PWM) block makes it possible for the CPU to control power converters, resistive loads, motors, etc., without using many CPU resources in tight timer loops. A universal asynchronous receiver/transmitter (UART) block makes it possible to receive and transmit data over a serial line with very little load on the CPU. Dedicated on chip hardware also often includes capabilities to communicate with other devices (chips) in digital formats such as Inter Integrated Circuit (I²C), Serial Peripheral Interface (SPI), Universal Serial Bus (USB), and Ethernet.

Microcontrollers were originally programmed only in assembly language, but various high level programming languages, such as C, Python and JavaScript, are now also in common use to target microcontrollers and embedded systems. Compilers for general purpose languages will typically have some restrictions as well as enhancements to better support the unique characteristics of microcontrollers. Some microcontrollers have environments to aid developing certain types of applications. Microcontroller vendors often make tools freely available to make it easier to adopt their hardware. Microcontrollers with specialty hardware may require their own non standard dialects of C, such as SDCC for the 8051, which prevent using standard tools (such as code libraries or static analysis tools) even for code unrelated to hardware features. Interpreters may also contain nonstandard features, such as MicroPython, although a fork, CircuitPython, has looked to move hardware dependencies to libraries and have the language adhere to a more CPython standard. Interpreter firmware is also available for some microcontrollers. For example, BASIC on the early microcontroller Intel 8052; BASIC and FORTH on the Zilog Z8 as well as some modern devices. Typically these interpreters support interactive programming. Simulators are available for some microcontrollers. These allow a developer to analyze what the behavior of the microcontroller and their program should be if they were using the actual part. A simulator will show the internal processor state and also that of the outputs, as well as allowing input signals to be generated. While on the one hand most simulators will be limited from being unable to simulate much other hardware in a system, they can exercise conditions that may otherwise be hard to reproduce at will in the physical implementation, and can be the quickest way to debug and analyze problems. Recent microcontrollers are often integrated with on chip debug circuitry that when accessed by an in circuit emulator (ICE) via JTAG, allow debugging of the firmware with a debugger. A real time ICE may allow viewing and/or manipulating of internal states while running. A tracing ICE can record executed program and MCU states before/after a trigger point.

Two different kinds of memory are commonly used with microcontrollers, a non volatile memory for storing firmware and a read write memory for temporary data.

From the earliest microcontrollers to today, six transistor SRAM is almost always used as the read/write working memory, with a few more transistors per bit used in the register file. In addition to the SRAM, some microcontrollers also have internal EEPROM and/or NVRAM for data storage; and ones that do not have any (such as the BASIC Stamp), or where the internal memory is insufficient, are often connected to an external EEPROM or flash memory chip. A few microcontrollers beginning in 2003 have "self programmable" flash memory.

The earliest microcontrollers used mask ROM to store firmware. Later microcontrollers (such as the early versions of the Freescale 68HC11 and early PIC microcontrollers) had EPROM memory, which used a translucent window to allow erasure via UV light, while production versions had no such window, being OTP (one time programmable). Firmware updates were equivalent to replacing the microcontroller itself, thus many products were not upgradeable. Motorola MC68HC805 was the first microcontroller to use EEPROM to store the firmware. EEPROM microcontrollers became more popular in 1993 when Microchip introduced PIC16C84 and Atmel introduced an 8051 core microcontroller that was first one to use NOR Flash memory to store the firmware. Today's microcontrollers almost all use flash memory, with a few models using FRAM and some ultra low cost parts still using OTP or Mask ROM.