1.MCU
A microcontroller (or MCU) is a computer-on-a-chip. It is a type of microprocessor emphasizing self-sufficiency and cost-effectiveness, in contrast to a general-purpose microprocessor (the kind used in a PC).

The majority of computer 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. For example, most embedded systems lack keyboards, screens, disks, printers, or other recognizable I/O devices of a personal computer. They may control electric motors, relays or voltages, and read switches, variable resistors or other electronic devices. Often, the only I/O device readable by a human is a single light-emitting diode, and severe cost or power constraints can even eliminate that.
單片機即單片微型計算機，是把中央處理器、存儲器、定時/計數(shù)器、輸入輸出接口都集成在一塊集成電路芯片上的微型計算機。與應(yīng)用在個人電腦中的通用型微處理器相比，它更強調(diào)自供應(yīng)（不用外接硬件）和節(jié)約成本。它的最大優(yōu)點是體積小，可放在儀表內(nèi)部，但存儲量小，輸入輸出接口簡單，功能較低。由于其發(fā)展非常迅速，舊的單片機的定義已不能滿足，所以在很多應(yīng)用場合被稱為范圍更廣的微控制器，但是目前在中國大陸仍多沿用“單片機”的稱呼。

絕大多數(shù)現(xiàn)在的單片機都是基于馮•諾伊曼結(jié)構(gòu)的，這種結(jié)構(gòu)清楚地定義了嵌入式系統(tǒng)所必需的四個基本部分：一個中央處理器核心，程序存儲器（只讀存儲器或者閃存）、數(shù)據(jù)存儲器（隨機存儲器），一個或者更多的定時/計時器，還有用來與外圍設(shè)備以及擴(kuò)展資源進(jìn)行通信的輸入/輸出端口——所有這些都被集