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• 小托0207

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  ;lt;br />systemdesign.blogspot.com/2007/12/embedded-system-for-automatic-washing.html
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  全自动洗衣机软件
  automatic washing-machine software
  
  A microcontroller (also MCU or µC) is a computer-on-a-chip, containing a processor, memory, and input/output functions. It is a microprocessor emphasizing high integration, in contrast to a general-purpose microprocessor (the kind used in a PC). In addition to the usual arithmetic and logic elements of a general purpose microprocessor, the microcontroller integrates additional elements such as read-write memory for data storage, read-only memory for program storage, EEPROM for permanent data storage, peripheral devices, and input/output interfaces. At clock speeds of as little as a few MHz or even lower, microcontrollers often operate at very low speed compared to modern day microprocessors, but this is adequate for typical applications. They consume relatively little power (milliwatts), and will generally have the ability to sleep while waiting for an interesting peripheral event such as a button press to wake them up again to do something. Power consumption while sleeping may be just nanowatts, making them ideal for low power and long lasting battery applications.
  
  Microcontrollers are frequently used in automatically controlled products and devices, such as automobile engine control systems, remote controls, office machines, appliances, power tools, and toys. By reducing the size, cost, and power consumption compared to a design using a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to electronically control many more processes.
  
  Embedded design
  The majority of computer systems 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, LEDs, small or custom LCD 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.
  
  [edit] Interrupts
  Microcontrollers must provide real time response to events in the 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). The ISR 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, an analogue to digital conversion completing, 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 also wake a microcontroller from a low power sleep state where the processor is halted until required to do something by a peripheral event.
  
  [edit] Programs
  Microcontroller programs must fit in the available on-chip program memory, since it would be costly to provide a system with external, expandable, memory. Compilers and assembly language are used to turn high-level language programs 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 program memory may be field-alterable flash or erasable read-only memory.
  
  [edit] Other microcontroller features
  Since embedded processors are usually used to control devices, they sometimes need to accept input from the device they are controlling. This is the purpose of the analog to digital converter. Since processors are built to interpret and process digital data, i.e. 1's and 0's, they won't be able to do anything with the analog signals that may be being 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. There is also a digital to analog converter that allows the processor to send data to the device it is controlling.
  
  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, or PIT for short. A PIT just counts down from some value to zero. Once it reaches zero, it sends an interrupt to the processor indicating that it has finished counting. This is useful for things 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.
  
  Another feature is the time processing unit or TPU for short. It is essentially just another timer, but more sophisticated. In addition to counting down, the TPU can detect input events, generate output events, and other useful operations that are beyond the scope of this discussion.
  
  [edit] Higher integration
  In contrast to general-purpose CPUs, microcontrollers may not implement an external address 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 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. Even if the cost of a CPU that has integrated peripherals is slightly more than the cost of a CPU + 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 microcontroller is a single integrated circuit, commonly with the following features:
  
  central processing unit - ranging from small and simple 4-bit processors to complex 32- or 64-bit processors
  discrete input and output bits, allowing control or detection of the logic state of an individual package pin
  serial input/output such as serial ports (UARTs)
  other serial communications interfaces like I²C, Serial Peripheral Interface and Controller Area Network for system interconnect
  peripherals such as timers, event counters, PWM generators, and watchdog
  volatile memory (RAM) for data storage
  ROM, EPROM, EEPROM or Flash memory for program and operating parameter storage
  clock generator - often an oscillator for a quartz timing crystal, resonator or RC circuit
  many include analog-to-digital converters
  in-circuit programming and debugging support
  This integration drastically reduces the number of chips and the amount of wiring and circuit board space 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. Microcontrollers have proved to be highly popular in embedded systems since their introduction in the 1970s.
  
  Some microcontrollers use a Harvard 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 microcontroller instruction set usually has many instructions intended for bit-wise operations to make control programs more compact. For 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 microcontroller could have a single instruction that would provide that commonly-required function.
  
  Microcontrollers typically do not have a math coprocessor, so multiplication and division are carried out using a standard library, or the faster and more compact Horner method.
  
  [edit] Volumes
  About 55% of all CPUs sold in the world are 8-bit microcontrollers. Over 2 billion 8-bit microcontrollers were sold in 1997. [1]
  
  Another 10% of all CPUs sold in the world are more specialized digital signal processors (DSPs). [2]
  
  Microcontrollers take the largest share of sales in the wider microprocessor market. Over 50% are "simple" controllers, and another 20% are more specialized digital signal processors (DSPs)[citation needed]. A typical home in a developed country is likely to have only one or two general-purpose microprocessors but somewhere ween one and two dozen microcontrollers. A typical mid range automobile has as many as 50 or more microcontrollers. They can also be found in almost any electrical device: washing machines, microwave ovens, telephones etc.
  
  Manufacturers have often produced special versions of their microcontrollers in order to help the hardware and software development of the target system. These have included EPROM versions that have a "window" on the top of the device through which program memory can be erased by ultra violet light, ready for reprogramming after a programming ("burn") and test cycle.
  
  An economical option for intermediate levels of production (usually a few score to a few thousand parts) is a one-time programmable (OTP) microcontroller. This uses the same die as the UV EPROM version of the part, and is programmed on the same equipment, but the package does not include the expensive quartz window required to admit UV light on to the chip.
  
  Other versions may be available where the ROM is accessed as an external device rather than as internal memory. A simple EPROM programmer, rather than a more complex and expensive microcontroller programmer, may then be used, however there is a potential loss of functionality through pin outs being tied up with external memory addressing rather than for general input/output. These kind of devices usually carry a higher cost but if the target production quantities are small, certainly in the case of a hobbyist, they can be the most economical option compared with the set up charges involved in mask programmed devices.
  
  A more rarely encountered development microcontroller is the "piggy back" version. This device has no internal ROM memory; instead pin outs on the top of the microcontroller form a socket into which a standard EPROM program memory device may be installed. The benefit of this approach is the release of microcontroller pins for input and output use rather than program memory. These kinds of devices are normally expensive and are impractical for anything but the development phase of a project or very small production quantities.
  
  The use of field-programmable devices on a microcontroller 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 a large number of systems will be made (say, several thousand), the cost of a mask-programmed memory is amortized over all products sold. A simpler integrated circuit process is used, and the contents of the read-only memory are set in the last step of chip manufacture instead of after assembly and test. However, mask-programmed parts cannot be updated in the field. If product firmware updates are still contemplated, a socket may be used to hold the controller which can then be replaced by a service technician, if required.
  
  [edit] Programming environments
  Microcontrollers were originally programmed only in assembly language, but various high-level programming languages are 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 the C programming language. Compilers for general purpose languages will typically have some restrictions as well as enhancements to ter support the unique characteristics of microcontrollers.
  
  Interpreter firmware is also available for some microcontrollers. The Intel 8052 and Zilog Z8 were available with BASIC very early on, and BASIC is more recently used in the BASIC Stamp MCUs.
  
  Some microcontrollers have environments to aid developing certain types of applications, e.g. Analog Device's Blackfin processors with the LabVIEW environment and its programming language "G".
  
  Simulators are available for some microcontrollers, such as in Microchip's MPLAB environment. These allow a developer to analyse what the behaviour 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 analyse problems.
  
  Recent microcontrollers integrated with on-chip debug circuitry accessed by In-circuit emulator via JTAG enables a programmer to debug the software of an embedded system with a debugger.
  
  [edit] Interrupt latency
  In contrast to general-purpose computers, microcontrollers used in embedded systems often seek to minimize interrupt latency over instruction throughput.
  
  When an electronic device causes an interrupt, the intermediate results, the registers, have to be saved before the software responsible for handling the interrupt can run, and then must be put back after it is finished. If there are more registers, this saving and restoring process takes more time, increasing the latency.
  
  Low-latency MCUs generally have relatively few registers in their central processing units, or they have "shadow registers", a duplicate register set that is only used by the interrupt software.
  
  The first microcontroller was the Intel 8048, released in 1976.
  
  The popularity of microcontrollers increased when EEPROM memory was incorporated to replace one time programmable PROM memory. With EEPROM, the development cycle of programming, testing and erasing a part could be repeated many times with the same part until the firmware was debugged and ready for production use.
  
  Nowadays microcontrollers are low cost and readily available for hobbyists.
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  Embedded System for Automatic Washing Machine using Microchip PIC18F Series Microcontroller
  The design uses the PIC18F series microcontroller. All the control functionalities of the system are built around this. Upgradeability is the unique feature of this system. Control card hardware and software allows the manufacturer to add or remove the features as per customer requirement and model. Thus once the whole system is designed it is very economic in large quantity production. Single-phase motor is considered for the design. Front panel consists of a keypad and LCD display. Keypad provides automatic and manual wash options to the user. LCD display is convenient to convey machine information to user. One more design possibility is to use brushless DC motors or three phase induction motor. These types of motors are very efficient but requires complex control algorithm. To implement such a complex and real time algorithm dedicated controller and software is required which a master controller controls. Even though cost is important criteria modern washing machines are designed with BLDC motors owing to efficiency and energy conservation. But in this assignment single phase universal motor has been used to design prototype due to its simplicity.
  
  Design Specifications
  
  This include both hardware and software specifications.
  
  The system should provide fully automatic mode, semi-automatic mode and manual mode. Modes should be selectable by a keypad.
  Under fully automatic mode user intervention requirement should be zero. Once the system is started in this mode it should perform its work independently and after the completion of work it should notify the user about the completion of work. This mode instantaneously should sense cloth quality and requirement of water, water temperature, detergent, load, wash cycle time and perform operation accordingly.
  In semi-automatic mode also user requirement should be nil. But user has to choose any one of the semi-automatic mode in which washing conditions are predefined. Once the predefined mode is started the system should perform its job and after completion it should inform the user.

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  在中国期刊网
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