【導(dǎo)讀】AT89C51是美國ATMEL公司生產(chǎn)的低電壓，高性能CMOS8位單片機，場合，可靈活應(yīng)用于各種控制領(lǐng)域。S-51產(chǎn)品指令系統(tǒng)完全兼容。4K字節(jié)可重復(fù)寫flash閃速存儲器。級加密程序存儲器。功耗空閑和掉電模式。RAM，32個I/O口線，兩個16位定時／計數(shù)器，一個5向量兩級中斷結(jié)構(gòu)，一個全雙工串行通信口，片內(nèi)振蕩器及時鐘電路。同時，AT89C51可降至0HZ. 的靜態(tài)邏輯操作，并支持兩種軟件可選的節(jié)電工作模式。工作，但允許RAM，定時／計數(shù)器，串行通信口及中斷系統(tǒng)繼續(xù)工作。作為輸出口用時，每位能吸收電流的方式驅(qū)動8個邏輯門電路，對端口寫“1”。和數(shù)據(jù)總線復(fù)用，在訪問期間激活內(nèi)部上拉電阻。電阻把端口拉到高電平，此時可做熟出口。Flash編程和程序校驗期間，P1接受低8位地址。位，可禁止ALE操作。和XTAL2分別是該放大器的輸入端和輸出端。構(gòu)成并聯(lián)振蕩電路。這種情況下，外部時鐘脈沖接到XTAL1端，即。平持續(xù)時間應(yīng)符合產(chǎn)品技術(shù)要求?；?，即可終止空閑工作模式。程序會首先響應(yīng)中斷，進入中斷服

　　

【正文】 ithout a reset, the latch initializes to a random value, and holds that value until reset is activated. It is necessary that the latched value of EA be in agreement with the current logic level at that pin in order for the device to function properly. Programming the Flash The AT89C51 is normally shipped with the onchip Flash memory array in the erased state (that is, contents = FFH) and ready to be programmed. The programming interface accepts either a highvoltage (12volt) or a lowvoltage (VCC) program enable signal. The low voltage programming mode provides a convenient way to program the AT89C51 inside the user’s system, while the highvoltage programming mode is patible with conventional third party Flash or EPROM programmers. The AT89C51 is shipped with either the highvoltage or lowvoltage programming mode enabled. The respective topside marking and device signature codes.. The AT89C51 code memory array is programmed bytebybyte in either programming mode. To program any nonblank byte in the onchip Flash Programmable and Erasable Read Only Memory, the entire memory must be erased using the Chip Erase Mode. Programming Algorithm Before programming the AT89C51, the address, data and control signals should be set up according to the Flash programming mode table and Figures 3 and 4. To program the AT89C51, take the following steps. 1. Input the desired memory location on the address lines. 2. Input the appropriate data byte on the data lines. 3. Activate the correct bination of control signals. AT89C51 MCU Introduction 第 14 頁（共 15 頁） 4. Raise EA/VPP to 12V for the highvoltage programming mode. 5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The bytewrite cycle is selftimed and typically takes no more than ms. Repeat steps 1 through 5, changing the address and data for the entire array or until the end of the object file is reached. Data Polling: The AT89C51 features Data Polling to indicate the end of a write cycle. During a write cycle, an attempted read of the last byte written will result in the plement of the written datum on . Once the write cycle has been pleted, true data are valid on all outputs, and the next cycle may begin. Data Polling may begin any time after a write cycle has been initiated. Ready/Busy: The progress of byte programming can also be monitored by the RDY/BSY output signal. is pulled low after ALE goes high during programming to indicate BUSY. is pulled high again when programming is done to indicate READY. Program Verify:If lock bits LB1 and LB2 have not been programmed, the programmed code data can be read back via the address and data lines for verification. The lock bits cannot be verified directly. Verification of the lock bits is achieved by observing that their features are enabled. Chip Erase: The entire Flash Programmable and Erasable Read Only Memory array is erased electrically by using the proper bination of control signals and by holding ALE/PROG low for 10 ms. The code array is written with all “1”s. The chip erase operation must be executed before the code memory can be reprogrammed. Reading the Signature Bytes: The signature bytes are read by the same procedure as a normal verification of locations 030H, 031H, and 032H, except that and must be pulled to a logic low. The values returned are as follows. (030H) = 1EH indicates manufactured by Atmel (031H) = 51H indicates 89C51 (032H) = FFH indicates 12V programming (032H) = 05H indicates 5V programming Programming Interface:Every code byte in the Flash array can be written and the AT89C51 MCU Introduction 第 15 頁（共 15 頁） entire array can be erased by using the appropriate bination of control signals. The write operation cycle is selftimed and once initiated, will automatically time itself to pletion.