【正文】
peripherals for puter systems. These are called embedded systems. While some embedded systems are very sophisticated, many have minimal requirements for memory and program length, with no operating system, and low software plexity. 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 puter, and may lack human interaction devices of any kind. It is mandatory that microcontrollers provide real time 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). 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, pleting an analog to digital conversion, a logic level change on an input such as from a button being pressed, and data received on a munication 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. Microcontroller programs must fit in the available onchip program memory, since it would be costly to provide a system with external, expandable, memory. Compilers and assembly language are used to turn highlevel language programs into a pact machine code for storage in the microcontroller39。 2 外文: MCU A microcontroller (or MCU) is a puteronachip. It is a type of microprocessor emphasizing selfsufficiency and costeffectiveness, in contrast to a generalpurpose microprocessor (the kind used in a PC). The majority of puter systems in use today are embedded in other machinery, such as telephones, clocks, appliances, vehicles, and infrastructure. An embedded system usually has minimal requirements for memory and program length and may require simple but unusual input/output systems.