Microcontroller Embedded Memory Technology Information Technology Essay

Micro chastenessler embed Memory engineering Information Technology EssayAmicro supportleris a small reckoner on a singleintegrated circuitcontaining a cardinal mainframe core, depot, and designm suitable excitant/ end productperipherals. Program retentivity in the form ofNOR chargeorOTP ROMis in whatsoever case much take ond on assay, as well as a typically small amount ofRAM. Microcontrollers be designed for plant applications, in distinguish to themicro central processors utilise inpersonal computersor new(prenominal) superior general purpose applications. http//upload.wikimedia.org/wikipedia/commons/ finger/c/c7/153056995_5ef8b01016_o.jpg/230px-153056995_5ef8b01016_o.jpgMicrocontrollers be utilize in automatically controlled products and devices, much(prenominal) as automobile engine control out attracts, implantable medical devices, remote controls, office machines, appliances, office staff tools, and toys. By reducing the size of it of it and monetary value compargond to a design that usages a collapse microprocessor, stock, and input signal/output devices, microcontrollers attain it economical to digitally control even much(prenominal) devices and processes. abstr mapping signal microcontrollers ar common, integrating analog components sine qua noned to control non-digital electronic goernances. virtually microcontrollers may use four-bit words and operate at measure ratefrequencies as get-go as 4kHz, for low power consumption (milliwatts or microwatts). They will largely pass the ability to oblige functionality succession waiting for an event such as a press release press or early(a) interrupt power consumption while slee trammelg ( mainframe clock and closely peripherals off) may be just na like a shotatts, make galore(postnominal) of them well suited for broad lasting battery applications. contrary microcontrollers may serve performance- captious roles, where they may need to act to a greater extent wish adigital signal processor(DSP), with higher clock speeds and power consumption.Embedded designA microcontroller enkindle be considered a self-contained strategy with a processor, reposition and peripherals and thunder mug be utilize as an imbed system.1The majority of microcontrollers in use today atomic number 18 enter in former(a) machinery, such as automobiles, telephones, appliances, and peripherals for computer systems. These are calledembedded systems. date close to embedded systems are very sophisticated, numerous stool minimal requirements for repositing and program length, with no operating system, and low software product complexity. exemplary input and output devices include switches,relays,solenoids,LEDs, small or customliquid crystal displaydisplays, radio frequency devices, and sensors for entropy such as temperature, humidity, light take etc. Embedded systems normally name no key notice, screen, disks, printers, or other recognizable I/O devices of apersonal computer, and may neediness human interaction devices of some(prenominal) kind.InterruptsMicrocontrollers mustiness providereal beat(predictable, though not necessarily fast) response to events in the embedded system they are controlling. When real events occur, aninterruptsystem discharge signal the processor to suspend treat the current statement sequence and to begin aninterrupt service custom(ISR, or interrupt handler). The ISR will perform any bear on demand based on the source of the interrupt sooner returning to the overlord instruction sequence. Possible interrupt sources are device dependent, and oft measures include events such as an upcountry 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 operated devices, interrupts may alike wake a microcontroller from a low power sle ep state where the processor is halted until required to do something by a peripheral event.ProgramsMicrocontroller programs must fit in the available on- cheque program memory, since it would be costly to provide a system with outdoor(a), expandable, memory. Compilers and assemblers are used to convert high-level language and assembler language codes into a beseechmachine codefor storage in the microcontrollers memory. Depending on the device, the program memory may be permanent, read- and memory that commode only be programmed at the factory, or program memory may be field-alterable ostentation or erasable read-only memory.Other microcontroller featuresMicrocontrollers usually contain from some(prenominal) to dozens of general purpose input/output pins (GPIO). GPIO pins are software configurable to all 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 pin s can drive external devices such as LEDs or motors.Many embedded systems need to read sensors that produce analog signals. This is the purpose of theanalog-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 inpouring data into a form that the processor can recognize. A little common feature on some microcontrollers is adigital-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 course of timers as well. One of the most common types of timers is theProgrammable Interval Timer(PIT). A PIT may either count down from some value to zero, or up to the mental ability of the count evince, overflowing to zero. Once it reaches zero, it sends an interrupt to the processor indicating that it has finished counting. This is useable for devices such as thermostats, which periodically test the temperature around them to see if they need to turn the air conditioner on, the heater on, etc.Time Processing building block(TPU) is a sophisticated timer. In addition to counting down, the TPU can determine input events, generate output events, and perform other useful operations.A dedicatedPulse Width Modulation(PWM) block makes it come-at-able for the CPU to controlpower converters,resistiveloads,motors, etc., without using lots of CPU resources in tight timerloops.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 computer hardware in like manner often includes capabilities to communicate with other devices (chips) in digital formats such asI2Cand series Peripheral Interface(SPI).Higher integrationIn contrast to general-purpose CPUs, micro-controllers may not implement an external address or data bus as they integrate RAM and non-volatile memory on the comparable chip as the CPU. Using fewer pins, the chip can be placed in a much little, cheaper software.Integrating the memory and other peripherals on a single chip and testing them as a unit increases the cost of that chip, but often results in decreased net cost of the embedded system as a whole. all the same if the cost of a CPU that has integrated peripherals is slightly more than the cost of a CPU and external peripherals, having fewer chips typically allows a smaller and cheaper circuit board, and reduces the labor required to assemble and test the circuit board.A micro-controller is a singleintegrated circuit, commonly with the following featurescentral processing unit ranging from small and simple 4-bitprocessors to complex 32- or 64-bit processorsdiscrete input and output bits, allowing control or detection of the logic state of an individualistic package pinserialinput/outputsuch asserial ports(UARTs)otherserial communicationsinterfaceslikeIC,Serial Peripheral InterfaceandController Area Networkfor system connectperipheralssuch astimers, event counters,PWM generators, andwatchdogvolatile memory (RAM) for data storageROM,erasable programmable read-only memory,EEPROMorFlash memoryforprogramand operating disputation storageclock generator often an oscillator for a quartz measure crystal, resonator orRC circuitmany include analog-to-digital convertersin-circuit programming and debugging weatherThis integration drastically reduces the number of chips and the amount of wiring andcircuit boardspace that would be needed to produce equivalent systems using separate chips. Furthermore, and on low pin count devices in particular, each pin may interface to some(prenominal) internal peripherals, with the pin function selected by software. This allows a part to be used in a wider variety of applications than if pins had dedicated fun ctions. Micro-controllers run through proved to be highly popular inembedded systemssince their installation in the 1970s.Some microcontrollers use aHarvard computer architecture separate memory buses for book of instructions and data, allowing accesses to take place concurrently. Where a Harvard architecture is used, instruction words for the processor may be a contrasting bit size than the length of internal memory and registers for example 12-bit instructions used with 8-bit data registers.The decision of which peripheral to integrate is often difficult. The microcontroller vendors often trade operating frequencies and system design flexibility against time-to-market requirements from their customers and overall swallow system cost. Manufacturers fuddle to balance the need to minimize the chip size against additional functionality.Microcontroller architectures vary widely. Some designs include general-purpose microprocessor cores, with one or more ROM, RAM, or I/O function s integrated onto the package. Other designs are purpose built for control applications. A micro-controller instruction set usually has many instructions in extended for bit-wise operations to make control programs more compact.2For example, a general purpose processor might require several instructions to test a bit in a register and branch if the bit is set, where a micro-controller could have a single instruction to provide that commonly-required function.Microcontrollers typically do not have a maths coprocessor, sofloating pointarithmetic is performed by software.VolumesAbout 55% of allCPUssold in the world are8-bitmicrocontrollers and microprocessors. According to Semico, over four billion 8-bit microcontrollers were sold in 2006.3A typical base in a developed country is likely to have only four general-purpose microprocessors but around three dozen microcontrollers. A typical mid-range automobile has as many as 30 or more microcontrollers. They can also be found in many elec trical devices such as washing machines, microwave ovens, and telephones.http//upload.wikimedia.org/wikipedia/commons/thumb/1/18/PIC18F8720.jpg/220px-PIC18F8720.jpgAPIC18F8720microcontrollerin an 80-pinTQFPpackage.Manufacturers have often produced special versions of their microcontrollers in order to help the hardware andsoftware growthof the target system. Originally these includedEPROMversions that have a window on the top of the device through which program memory can be erased by invisiblelight, ready for reprogramming after a programming (burn) and test cycle. Since 1998, EPROM versions are rare and have been replaced byEEPROMandflash, which are easier to use (can be erased electronically) and cheaper to manufacture.Other versions may be available where theROMis accessed as an external device rather than as internal memory, however these are turn increasingly rare due to the widespread availability of cheap microcontroller programmers.The use of field-programmable devices o n a microcontroller may allow field update of themicrocodeor 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 an economical option. These mask programmed parts have the program laid down in the same way as the logic of the chip, at the same time.Programming environmentsMicrocontrollers were originally programmed only inassembly language, but varioushigh-level programming languagesare now also in common use to target microcontrollers. These languages are either designed specially for the purpose, or versions of general purpose languages such as theC programming language.Compilersfor general purpose languages will typically have some restrictions as well as enhancements to better have the anomalous 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.Many microcontrollers are so quirky that they effectively require their own non-standard dialects of C, such asSDCC for the 8051, which retard using standard tools (such as code libraries or static compend tools) even for code unrelated to hardware features. Interpreters are often used to hide such low level quirks.Interpretermicrocode is also available for some microcontrollers. For example,BASICon the early microcontrollersIntel80524 BASIC and forwardon theZilog Z85as well as some modern devices. typically these interpreters supportinteractive programming.Simulatorsare available for some microcontrollers, such as in MicrochipsMPLABenvironment. 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-chipdebugcircuitry that when accessed by anin-circuit emulatorviaJTAG, allow debugging of the firmware with adebugger.Types of microcontrollersFreescale 68HC11(8-bit)Intel 8051ARMprocessors (from many vendors) usingARM7or Cortex-M3 cores are generally microcontrollersSTMicroelectronicsSTM8(8-bit),ST10(16-bit) andSTM32(32-bit)AtmelAVR(8-bit),AVR32(32-bit), andAT91SAM(32-bit)FreescaleColdFire(32-bit) andS08(8-bit)Hitachi H8,Hitachi SuperH(32-bit)HyperstoneE1/E2 (32-bit, First full integration ofRISCandDSPon one processor core 19961)MIPS(32-b it PIC32)NEC V850(32-bit)PIC(8-bit PIC16, PIC18, 16-bit dsPIC33 / PIC24)PowerPCISEPSoC (Programmable System-on-Chip)Rabbit 2000(8-bit)Texas Instruments MicrocontrollersMSP430(16-bit), C2000 (32-bit), and Stellaris (32-bit)Toshiba TLCS-870(8-bit/16-bit)Zilog eZ8(16-bit),eZ80(8-bit)and many others, some of which are used in very narrow range of applications or are more like applications processors than microcontrollers. The microcontroller market is extremely fragmented, with numerous vendors, technologies, and markets. lineage that many vendors sell (or have sold) multiple architectures.Interrupt latencyIn contrast to general-purpose computers, microcontrollers used in embedded systems often try out to optimizeinterrupt latencyover instruction throughput. Issues include both reducing the latency, and making it be more predictable (to support real time control).When an electronic device causes an interrupt, the intermediate results (registers) have to be saved before the software re sponsible for handling the interrupt can run. They must also be re pedigreed after that software is finished. If there are more registers, this economy and restoring process takes more time, increasing the latency. Ways to reduce such scene/restore latency include having relatively few registers in their central processing units (undesirable because it slows down most non-interrupt processing substantially), or at to the lowest degree having the hardware not save them all (this fails if the software then necessitate to compensate by saving the rest manually). Another proficiency involves spend silicon gates on shadow registers one or more duplicate registers used only by the interrupt software, perhaps living a dedicated stack.Other factors affecting interrupt latency includeCycles needed to complete current CPU activities. To minimize those costs, microcontrollers tend to have short pipelines (often three instructions or less), small economize buffers, and chink that longer instructions are continuable or restartable.RISCdesign principles vouch that most instructions take the same number of cycles, helping ward off the need for most such continuation/restart logic.The length of any scathing sectionthat needs to be interrupted. Entry to a critical section restricts concurrent data bodily structure access. When a data structure must be accessed by an interrupt handler, the critical section must block that interrupt. Accordingly, interrupt latency is increased by however long that interrupt is blocked. When there are hard external constraints on system latency, developers often need tools to measure interrupt latencies and track down which critical sections cause slowdowns.One common technique just blocks all interrupts for the duration of the critical section. This is easy to implement, but sometimes critical sections get uncomfortably long.A more complex technique just blocks the interrupts that may sparkle access to that data structure. This often based on interrupt priorities, which tend to not correspond well to the relevant system data structures. Accordingly, this technique is used mostly in very constrained environments.Processors may have hardware support for some critical sections. Examples include supporting atomic access to bits or bytes within a word, or other atomic access primitives like theLDREX/STREXexclusive access primitives introduced in theARMv6architecture.Interrupt nesting. Some microcontrollers allow higher priority interrupts to interrupt lower priority ones. This allows software to manage latency by giving time-critical interrupts higher priority (and hence lower and more predictable latency) than less-critical ones.Trigger rate. When interrupts occur back-to-back, microcontrollers may bar an extra context save/restore cycle by a form oftail calloptimization.Lower end microcontrollers tend to support fewer interrupt latency controls than higher end ones.HistoryThe start single-chip microprocessor w as the 4-bitIntel 4004released in 1971. With theIntel 8008and more capable microprocessors available over the next several years.These however all required external chip(s) to implement a working(a) system, raising total system cost, and making it impossible to economically computerise appliances.The first computer system on a chip optimized for control applications was theIntel 8048released in 1975,citation with bothRAMandROMon the same chip. This chip would find its way into over one billion PC keyboards, and other numerous applications. At this time Intels President, Luke J. Valenter, stated that the (Microcontroller) was one of the most sure-fire in the companies history, and expanded the divisions budget over 25%.Most microcontrollers at this time had two variants. One had an erasableEPROMprogram memory, which was significantly more expensive than thePROMvariant which was only programmable once.In 1993, the introduction ofEEPROMmemory allowed microcontrollers (beginning wit h the MicrochipPIC16x84)2citation needed) to be electrically erased quickly without an expensive package as required forEPROM, allowing both rapid prototyping, andIn System Programming.The same year, Atmel introduced the first microcontroller usingFlash memory.6Other companies rapidly followed suit, with both memory types.Cost has plummeted over time, with the cheapest 8-bit microcontrollers being available for under $0.25 in sum of money (thousands) in 2009,citation neededand some 32-bit microcontrollers around $1 for similar quantities.Nowadays microcontrollers are low cost and readily available for hobbyists, with large online communities around certain processors.In the future,MRAMcould potentially be used in microcontrollers as it has unnumbered endurance and its incremental semiconductor wafer process cost is relatively low.Microcontroller embedded memory technologySince the emergence of microcontrollers, many different memory technologies have been used. Almost all microcon trollers have at least two different kinds of memory, a non-volatile memory for storing firmware and a read-write memory for temporary data. informationFrom 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 theregister file.MRAMcould potentially replace it as it is 4-10 times denser which would make it more cost effective.In addition to the SRAM, some microcontrollers also have internal EEPROM for data storage and even ones that do not have any (or not enough) are often connected to external serial EEPROM chip (such as theBASIC Stamp) or external serial flash memory chip.A few recent microcontrollers beginning in 2003 have self-programmable flash memory6.FirmwareThe earliest microcontrollers used hard-wired or mask ROM to store firmware. Later microcontrollers (such as the early versions of theFreescale 68HC11and earlyPIC microcontrollers) had quartz windows that allowed ult raviolet light in to erase theEPROM.The MicrochipPIC16C84, introduced in 1993,7was the first microcontroller to useEEPROMto store firmware.Also in 1993, Atmel introduced the first microcontroller usingNOR Flash memoryto store firmware.6PSoCmicrocontrollers, introduced in 2002, store firmware inSONOSflash memory.MRAMcould potentially be used to store firmware.