Now, we use a single chip microcomputer to complete the above process. Obviously, it must first have a component to replace the abacus, which is the "arithmetic unit"; Secondly, there should be devices that can play the role of paper and pen, that is, they can remember the original topics, original data and intermediate results, and also remember various commands that enable the single chip microcomputer to automatically calculate. Such devices are called "memory". In addition, a controller that can replace human action is needed, which can send various control signals according to the given command in advance, so that the whole calculation process can be carried out step by step. However, these three parts alone are not enough. The original data and commands need to be input and the calculation results need to be output in order, sometimes waiting.
In the above example, when calculating 163 × 156, the number 36 cannot enter the arithmetic unit at the same time. Therefore, it is necessary to set a "door" to act according to the command of the controller on the single chip microcomputer, and let new data enter when the arithmetic unit needs it. Or, when the arithmetic unit gets the final result, it outputs the result, and the intermediate result can not be "slipped out" of the single chip microcomputer. This kind of "gate" circuit which manages the input and output data is called "port" in single chip microcomputer. In the single chip microcomputer, there are basically three types of information flowing. One is data, that is, various original data (such as 36, 163, etc. in the above example), intermediate results (such as quotient 4, remainder 30, etc. obtained by 166 ÷ 34), programs (sets of commands), etc. In this way, the external equipment enters the single chip microcomputer through the "port" and then stores it in the memory. In the process of operation and processing, the data is read from the memory into the arithmetic unit for operation, and the intermediate results of the operation shall be stored in the memory, or finally output by the arithmetic unit through the "port".
The various commands (programs) that the user wants the single chip microcomputer to execute are also sent to the controller in the form of data from the memory. After being interpreted (decoded) by the controller, they are changed into various control signals in order to execute various commands with functions such as addition, subtraction, multiplication and division. Therefore, this kind of information is called control command, that is, the controller controls the arithmetic unit to carry out operation and processing step by step, and also controls the reading (taking out data) and writing (storing data) of the memory. The third type of information is address information, which is used to tell the arithmetic unit and controller where to get the command and data, where to store the results, through which port to input and output information, etc.
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Memory is divided into read-only memory and read-write memory. The former stores debugged fixed programs and constants, and the latter stores some data that may change at any time. As the name suggests, once the read-only memory stores the data, it can only read out and cannot be changed (EPROM, E2PROM and other types of ROM can change and write data through certain methods - editor's note). The read-write memory can store or read data at any time.
In fact, people often combine the arithmetic unit and controller, which is called the central processing unit - CPU. In addition to the operation, the single chip microcomputer should also complete the control function. Therefore, it is inseparable from counting and timing. Therefore, a timer and counter are set in the single chip microcomputer. So far, we have known the basic composition of single chip microcomputer, that is, single chip microcomputer is composed of central processing unit (i.e. arithmetic unit and controller in CPU), read-only memory (usually expressed as ROM), read-write memory (also known as random memory, usually expressed as RAM), input / output port (also divided into parallel port and serial port, expressed as I / O port), etc. In fact, there is a clock circuit in the single chip microcomputer, so that the single chip microcomputer can operate and control rhythmically. In addition, there is the so-called "interrupt system", which has the function of "communication room". When the parameters of the single-chip microcomputer control object reach a state that needs to be intervened, it can be reported to the CPU through this "communication room", so that the CPU can take appropriate countermeasures according to the priorities of external events.
Now, we have known the composition of single chip microcomputer. The remaining problem is how to connect their parts into an interrelated whole? In fact, there is a "link" connecting them inside the single chip microcomputer, that is, the so-called "internal bus". This bus is like the "trunk road" of a big city, and CPU, ROM, ram, I / O port, interrupt system, etc. are distributed on both sides of this "bus" and connected with it. Thus, all instructions and data can be transmitted through the internal bus, just as all kinds of goods in a big city are transmitted through the trunk road.
