Microcontroller Embedded Memory Technology Information Technology Essay

Micro restraintler Embedded Memory Technology In formation Technology EssayAmicrocontrolleris a small computer on a singleintegrated circuitcontaining a mainframe core, memory, and programmemableinput/ productionperipherals. Program memory in the form ofNOR flashorOTP ROMis also practically take ond on chip, as intumesce as a typically small amount ofRAM. Microcontrollers argon designed for implant applications, in contrast to themicro act uponorsused in personalised computersor other prevalent theatrical role applications. http//upload.wikimedia.org/wikipedia/commons/thumb/c/c7/153056995_5ef8b01016_o.jpg/230px-153056995_5ef8b01016_o.jpgMicrocontrollers are used in automatically controlled products and thingmabobs, much(prenominal) as automobile engine control arrangements, implantable medical devices, remote controls, office machines, appliances, military group tools, and toys. By reducing the size of it and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control level more devices and processes. Mixed signal microcontrollers are common, combine analog components needed to control non-digital electronic systems. both(prenominal) microcontrollers may use four-bit words and operate atclock ratefrequencies as lower-ranking as 4kHz, for low power consumption (milliwatts or microwatts). They will generally shake up 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 almost peripherals off) may be clean nanowatts, making legion(predicate) of them well suited for long lasting battery applications. different microcontrollers may serve performance-critical roles, where they may need to act more homogeneous adigital signal processor(DSP), with higher clock speeds and power consumption.Embedded designA microcontroller tush be considered a self-containe d system with a processor, memory and peripherals and ignore be used as anembedded system.1The majority of microcontrollers in use today are embedded in other machinery, such as automobiles, telephones, appliances, and peripherals for computer systems. These are calledembedded systems. While some embedded systems are very sophisticated, umpteen aim minimal requirements for memory and program length, with no operating system, and low bundle compositeity. Typical input and output devices include switches,relays,solenoids,LEDs, small or customLCDdisplays, radio frequency devices, and sensors for entropy such as temperature, humidity, light level etc. Embedded systems usually put on no keyboard, screen, disks, printers, or other recognizable I/O devices of apersonal computer, and may lack human interaction devices of any kind.InterruptsMicrocontrollers must providereal time(predictable, though not necessarily fast) response to events in the embedded system they are controlling. W hen certain events occur, aninterruptsystem can signal the processor to susp block processing the current tuition sequence and to begin aninterrupt service number(ISR, or interrupt handler). The ISR will perform any processing require based on the source of the interrupt before re round of golfing to the original instruction sequence. Possible interrupt sources are device dependent, and often include events such as an inherent timer all overflow, completing an analog to digital conversion, a logical system 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 also wake a microcontroller from a low power sleep state where the processor is halted until indispensable to do something by a peripheral event.ProgramsMicrocontroller programs must fit in the available on-chip program memory, since it would be costly to provide a system with internation al, expandable, memory. Compilers and assemblers are used to convert high-level language and assembler language codes into a compactmachine codefor storage in the microcontrollers memory. Depending on the device, the program memory may be permanent, read-only memory that can only be programmed at the factory, or program memory may be eye socket-alterable flash or erasable read-only memory.Other microcontroller featuresMicrocontrollers usually contain from several to cardinals of general purpose input/output pins (GPIO). GPIO pins are package 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 outside signals. Configured to the output state, GPIO pins 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 incoming data into a form that the processor can recognize. A less 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 variety of timers as well. peerless 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 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, the heater on, etc.Time Processing Unit(TPU) is a sophist icated timer. In addition to counting down, the TPU can detect input events, pass on output events, and perform other useful operations.A dedicatedPulse Width Modulation(PWM) block makes it possible for the CPU to controlpower converters, immuneloads,motors, etc., without exploitation 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 also often includes capabilities to communicate with other devices (chips) in digital formats such asI2CandSerial Peripheral Interface(SPI).Higher consolidationIn contrast to general-purpose CPUs, micro-controllers may not implement an external holler or data bus as they integrate RAM and non-volatile memory on the same chip as the CPU. Using fewer pins, the chip can be placed in a much smaller, cheaper package.Integrating the memory and other peripherals on a single c hip 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. Even 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 individual package pinserialinput/outputsuch asserial ports(UARTs)otherserial communicationsinterfaces likeIC,Serial Peripheral InterfaceandController Area Ne twainrkfor system interconnectperipheralssuch astimers, event counters,PWM generators, andwatchdogvolatile memory (RAM) for data storageROM,EPROM,EEPROMor Flash memoryforprogramand operating arguing storageclock generator often an oscillator for a quartz timing crystal, resonator orRC circuitmany include analog-to-digital convertersin-circuit programming and correctging supportThis 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 several 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 functions. Micro-controllers have proved to be highly popular inembedded systemssince their introduction in the 1970s.Some microcontrollers use aHarvard architecture separate memory buses for instructions and data, allowing accesses to take place concurrently. Where a Harvard architecture is used, instruction words for the processor may be a different 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 lower system cost. Manufacturers have 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 functions integrated onto the package. Other designs are purpose built for control applications. A micro-controller instruction set usually has many instructions in feeded 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-con troller could have a single instruction to provide that commonly-required function.Microcontrollers typically do not have amath coprocessor, sofloating point arithmetic 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 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 as many as 30 or more microcontrollers. They can also be found in many electrical 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(prenominal) versions of their microcontrollers in order to help the hardware andsoftware developmentof the tar depart system. Originally these includedEPROMversions that have a window on the fade of the device through which program memory can be erased byultravioletlight, 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 becoming increasingly rare due to the widespread availability of cheap microcontroller programmers.The use of field-programmable devices on 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 overwhelm 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 in manufacture language, but varioushigh-level programming languagesare now also in common use to target microcontrollers. These languages are either designed in particular 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 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 consume their hardware.Many microcontrollers are so quirky that they effectively require their own non-standard dialects of C, such asSDCC for the 8051, which prevent using standa rd tools (such as code libraries or static analysis tools) even for code unrelated to hardware features. Interpreters are often used to hide such low level quirks.Interpreterfirmware is also available for some microcontrollers. For example,BASICon the early microcontrollersIntel80524 BASIC andFORTHon 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-bit 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. smell that many vendors sell (or have sold) multiple architectures.Interrupt latencyIn contrast to general-purpose computers, microcontrollers used in embedded systems often seek to optimiseinterrupt 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 responsible for handling the interrupt can run. They must also be concernd after that software is finished. If there are more registers, this saving and restoring process takes more time, increasing the latency. Ways to reduce such context/restore latency include having relatively few registers in their central processing units (undesirable becaus e it slows down most non-interrupt processing substantially), or at least having the hardware not save them all (this fails if the software then needs to compensate by saving the rest manually). Another technique involves spending silicon gates on shadow registers one or more duplicate registers used only by the interrupt software, perhaps supporting 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 write buffers, and ensure that longer instructions are continuable or restartable.RISCdesign principles ensure that most instructions take the same number of cycles, helping avoid the need for most such continuation/restart logic.The length of anycritical sectionthat needs to be interrupted. Entry to a critical section restricts concurrent data structure access. When a data structure must be accessed by an int errupt handler, the critical section must block that interrupt. Accordingly, interrupt latency is increase 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 gash 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 trigger 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 thus lower and more predictable latency) than less-critical ones.Trigger rate. When interrupts occur back-to-back, microcontrollers may avoid 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 commencement exercise single-chip microprocessor was 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 system, raising total system cost, and making it impossible to economically computerize appliances.The first computer system on a chip optimized for control applications was theInte l 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 successful 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 with 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 micro controllers being available for under $0.25 in quantity (thousands) in 2009,citation neededand some 32-bit microcontrollers around $1 for akin(predicate) 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 infinite 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 microcontrollers have at least two different kinds of memory, a non-volatile memory for storing firmware and a read-write memory for temporary data.DataFrom the early 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 dense r 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 ultraviolet 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.