【正文】 font table. 3 program memory (ROM): 8051 a total of 4096 8bit mask ROM used to store the user program, raw data, or form. 4 Timer / Counter (ROM): 8051 has two 16bit programmable timer / counter, to counter or timer interrupt is generated for the control program steering. 5 parallel input and output (I / O) port: 8051 a total of 4 groups of 8bit I / O port (P0, P1, P2 or P3) used for external data transfer. 6 fullduplex serial port: 8051 built a fullduplex serial munication port, serial data transfer used in conjunction with other devices, the serial port can be used for both asynchronous munication transceivers, when the synchronization shifter. 7 interrupt system: 8051 has better interrupt function, there are two external interrupts, two timer / counter interrupt and a serial interrupt, to meet the different control requirements, and has two priority selection. 8 clock circuit: 8051 builtin frequencies up to 12MHz clock circuit used to generate the pulse timing of the entire operation of a microcontroller, but need an external oscillator capacitor 8051.There are two types of the structure of the microcontroller, a form that is separate from the program memory and data memory, ., the structure of Harvard (Harvard), another is the use of program memory and data memory into one of the widely used generalpurpose puter structure, . Princeton (Princeton) structure. INTEL MCS51 series MCU is used in the form of a Harvard architecture. MCS51 Pin Description: MCS51 series singlechip 8031,8051 and 8751 40Pin package the double row directly DIP structure to the right is the pin configuration 40 pin Power and ground two external crystal oscillator the clock line two, four groups of 32 8 I / O port, interrupt port line P3port line multiplexing. Pin9: the RESET / VPD reset signals are multiplexed with their feet, when the 8051 is powered on, the clock circuit to work, the RESET pin high of more than 24 clock cycles, the system is initially reset. After initialization, the program counter (PC) point 0000H, all P0P3 output is high, the stack pointer write 07H other special register is cleared to 0. RESET is low down from the high, starting from address 0000H program execution. In the initial reset, however, does not change the state of the RAM (working registers R0R7), the initial state of 8051. 8051 reset can be automatically reset, it can be manually reset, as shown in Figure 25. In addition, the the RESET / Vpd or a plex with their feet during Vcc powerdown, this pin can be connected to the standby power to ensure the microcontroller internal RAM data is not lost.Pin30: ALE / when access to external program, ALE (address latch) output is used to latch the low byte address. Access to the internal program memory, ALE end there will be a 1/6 clock frequency of positive pulse signal, this signal can be used to identify the microcontroller is working, but also can be used as a clock output externally. More a feature when accessing external program memory, ALE will skip a pulse. If the MCU EPROM, programming the meantime, will be used to enter the programming pulse. Pin29: When accessing external program memory, this pin outputs a negative pulse strobe signal, the PC39。s 16bit address data will appear in P0 and P2 port, external program memory put instruction P0 port, read by the CPU and execute . Pin31: EA / the Vpp program memory, internal and external strobe line, 8051 and 8751 singlechip, builtin 4KB of program memory, when the EA is high and the program address less than 4kB, internal program memory read instruction data, and more than 4kB The address reads the external mand data. If the EA is low, regardless of the address size, always read the instruction from external memory. Obviously, the internal program memory 8031, EA end must be grounded. Programming EA / Vpp pin needs to be coupled with a programming voltage of 21V.附錄B8051單片機包含中央處理器、程序存儲器(ROM)、數(shù)據(jù)存儲器(RAM)、定時/計數(shù)器、并行接口、串行接口和中斷系統(tǒng)等幾大單元及數(shù)據(jù)總線、地址總線和控制總線等三大總線，現(xiàn)在我們分別加以說明：1. 中央處理器：中央處理器(CPU)是整個單片機的核心部件，是8位數(shù)據(jù)寬度的處理器，能處理8位二進制數(shù)據(jù)或代碼，CPU負責控制、指揮和調(diào)度整個單元系統(tǒng)協(xié)調(diào)的工作，完成運算和控制輸入輸出功能等操作。2. 數(shù)據(jù)存儲器(RAM)8051內(nèi)部有128個8位用戶數(shù)據(jù)存儲單元和128個專用寄存器單元，它們是統(tǒng)一編址的，專用寄存器只能用于存放控制指令數(shù)據(jù)，用戶只能訪問，而不能用于存放用戶數(shù)據(jù)，所以，用戶能使用的RAM只有128個，可存放讀寫的數(shù)據(jù)，運算的中間結(jié)果或用戶定義的字型表。3. 程序存儲器(ROM)：8051共有4096個8位掩膜ROM，用于存放用戶程序，原始數(shù)據(jù)或表格。4. 定時/計數(shù)器(ROM)：8051有兩個16位的可編程定時/計數(shù)器，以實現(xiàn)定時或計數(shù)產(chǎn)生中斷用于控制程序轉(zhuǎn)向。5. 并行輸入輸出(I/O)口：8051共有4組8位I/O口(P0、PP2或P3)，用于對外部數(shù)據(jù)的傳輸。6. 全雙工串行口：8051內(nèi)置一個全雙工串行通信口，用于與其它設(shè)備間的串行數(shù)據(jù)傳送，該串行口既可以用作異步通信收發(fā)器，也可以當同步移位器使用。7. 中斷系統(tǒng)：8051具備較完善的中斷功能，有兩個外中斷、兩個定時/計數(shù)器中斷和一個串行中斷，可滿足不同的控制要求，并具有2級的優(yōu)先級別選擇。8. 時鐘電路：8051內(nèi)置最高頻率達12MHz的時鐘電路，用于產(chǎn)生整個單片機運行的脈沖時序，但8051單片機需外置振蕩電容。單片機的結(jié)構(gòu)有兩種類型，一種是程序存儲器和數(shù)據(jù)存儲器分開的形式，即哈佛(Harvard)結(jié)構(gòu)，另一種是采用通用計算機廣泛使用的程序存儲器與數(shù)據(jù)存儲器合二為一的結(jié)構(gòu)，即普林斯頓(Princeton)結(jié)構(gòu)。INTEL的MCS51系列單片機采用的是哈佛結(jié)構(gòu)的形式。MCS51的引腳說明：MCS51系列單片機中的8038051及8751均采用40Pin封裝的雙列直接DIP結(jié)構(gòu)，右圖是它們的引腳配置，40個引腳中，正電源和地線兩根，外置石英振蕩器的時鐘線兩根，4組8位共32個I/O口，中斷口線與P3口線復用。Pin9：RESET/Vpd復位信號復用腳，當8051通電，時鐘電路開始工作，在RESET引腳上出現(xiàn)24個時鐘周期以上的高電平，系統(tǒng)即初始復位。初始化后，程序計數(shù)器PC指向0000H，P0P3輸出口全部為高電平，堆棧指針寫入07H，其它專用寄存器被清“0”。RESET由高電平下降為低電平后，系統(tǒng)即從0000H地址開始執(zhí)行程序。然而，初始復位不改變RAM(包括工作寄存器R0R7)的狀態(tài)，8051的初始態(tài)。8051的復位方式可以是自動復位，也可以是手動復位，見下圖25。此外，RESET/Vpd還是一復用腳，Vcc掉電其間，此腳可接上備用電源，以保證單片機內(nèi)部RAM的數(shù)據(jù)不丟失。Pin30：ALE/當訪問外部程序器時，ALE(地址鎖存)的輸出用于鎖存地址的低位字節(jié)。而訪問內(nèi)部程序存儲器時，ALE端將有一個1/6時鐘頻率的正脈沖信號，這個信號可以用于識別單片機是否工作，也可以當作一個時鐘向外輸出。更有一個特點，當訪問外部程序存儲器，ALE會跳過一個脈沖。如果單片機是EPROM，在編程其間，將用于輸入編程脈沖。Pin29：當訪問外部程序存儲器時，此腳輸出負脈沖選通信號，PC的16位地址數(shù)據(jù)將出現(xiàn)在P0和P2口上，外部程序存儲器則把指令數(shù)據(jù)放到P0口上，由CPU讀入并執(zhí)行。Pin31：EA/Vpp程序存儲器的內(nèi)外部選通線，8051和8751單片機，內(nèi)置有4kB的程序存儲器，當EA為高電平并且程序地址小于4kB時，讀取內(nèi)部程序存儲器指令數(shù)據(jù)，而超過4kB地址則讀取外部指令數(shù)據(jù)。如EA為低電平，則不管地址大小，一律讀取外部程序存儲器指令。顯然，對內(nèi)部無程序存儲器的8031，EA端必須接地。在編程時，EA/Vpp腳還需加上21V的編程電壓。附錄C1. 主電路2. 發(fā)射電路3. 實物圖33