通信工程專(zhuān)業(yè)英語(yǔ)論文

1、精選文檔The General Situation of AT89C51The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes of Flash Programmable and Erasable Read Only Memory (PEROM) and 128 bytes RAM. The device is manufactured using Atmels high density nonvolatile memory technology and is compatible

2、with the industry standard MCS-51 instruction set and pin out. The chip combines a versatile 8-bit CPU with Flash on a monolithic chip; the Atmel AT89C51 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications.Features: Compatibl

3、e with MCS-51 Products 4K Bytes of In-System Reprogrammable Flash Memory Endurance: 1,000 Write/Erase Cycles Fully Static Operation: 0 Hz to 24 MHz Three-Level Program Memory Lock 128 x 8-Bit Internal RAM 32 Programmable I/O Lines Two 16-Bit Timer/Counters Six Interrupt Sources Programmable Serial C

4、hannel Low Power Idle and Power Down Modes The AT89C51 provides the following standard features: 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator and clock circuitry. In additio

5、n, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power Down Mode saves the RAM c

6、ontents but freezes the oscillator disabling all other chip functions until the next hardware reset.Block DiagramPin Description:VCC Supply voltage. GND Ground.Port 0：Port 0 is an 8-bit open drain bidirectional I/O port. As an output port each pin can sink eight TTL inputs. When 1s are written to po

7、rt 0 pins, the pins can be used as high impedance inputs. (Sink/flow)Port 0 may also be configured to be the multiplexed low order address/data bus during accesses to external program and data memory. In this mode P0 has internal pull-ups. Port 0 also receives the code bytes during Flash programming

8、, and outputs the code bytes during program verification. External pull-ups are required during program verification.Port 1：Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled

9、high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. Port 1 also receives the low-order address bytes during Flash programming and verification.Port 2：Port 2 is an 8-bit bidire

10、ctional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) becaus

11、e of the internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that uses 16-bit addresses (MOVX DPTR). In this application it uses strong internal pull-ups when emitting 1s. During accesses to external data

12、 memories that use 8-bit addresses (MOVX RI), Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order address bits and some control signals during Flash programming and verification.Port 3：Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Th

13、e Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull-ups. Port 3 also serves the f

14、unctions of various special features of the AT89C51 as listed below:Port pinalternate functionsP3.0rxd (serial input port)P3.1txd (serial output port)P3.2int0 (external interrupt0)P3.3int1 (external interrupt1)P3.4t0 (timer0 external input)P3.5t1 (timer1 external input)P3.6 WR (external data memory

15、write strobe)P3.7rd (external data memory read strobe)Port 3 also receives some control signals for Flash programming and verification.RST：Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.ALE/PROG：Address Latch Enable output pulse for latching

16、the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming.In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, tha

17、t one ALE pulse is skipped during each access to external Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no

18、effect if the microcontroller is in external execution mode.PSEN：Program Store Enable is the read strobe to external program memory. When the AT89C51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each a

19、ccess to external data memory.EA/VPP：External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1(LB1) is programmed, EA will be internally latched (fasten with a

20、 latch) on reset. EA should be strapped to VCC for internal program executions. This pin also receives the 12-volt programming enable voltage（VPP) during Flash programming, for parts that require 12-volt VPP.XTAL1：Input to the inverting oscillator amplifier and input to the internal clock operating

21、circuit.XTAL2：Output from the inverting oscillator amplifier.Oscillator Characteristics：XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz crystal or ceramic resonator may b

22、e used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 2. There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip-flop, b

23、ut minimum and maximum voltage high and low times specifications must be observed.Idle Mode：In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain uncha

24、nged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware reset.It should be noted that when idle is terminated by a hard ware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal reset algor

25、ithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a port pin when Idle is terminated by reset, the instruction following the one that invokes Idle should not be one

26、that writes to a port pin or to external memory.Status of External Pins During Idle and Power Down ModesmodeProgram memoryALEpsenPort0 Port1Port2Port3idleinternal11datadatadataDataIdleExternal11floatDatadataDataPower downInternal00DataDataDataDataPower downExternal 00floatdataDatadataPower Down Mode

27、In the power down mode the oscillator is stopped, and the instruction that invokes power down is the last instruction executed. The on-chip RAM and Special Function Registers retain their values until the power down mode is terminated. The only exit from power down is a hardware reset. Reset redefin

28、es the SFRs but does not change the on-chip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize.Program Memory Lock BitsOn the chip are three lock bits which can be left unpro

29、grammed (U) or can be programmed (P) to obtain the additional features listed in the table below: Lock Bit Protection ModesProgram lock bitsProtection typeLb1 Lb2Lb31UUUNo program lock features2PUUMovc instructions executed from external program memory are disable from fetching code bytes from inter

30、nal memory, ea is sampled and latched on reset, and further programming of the flash disabled3PPUSame as mode 2, also verify is disable.4PPPSame as mode 3, also external execution is disabled.When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched during reset. If the dev

31、ice is powered up without 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 AT89

32、C51 is normally shipped with the on-chip Flash memory array in the erased state (that is, contents = FFH) and ready to be programmed. The programming interface accepts either a high-voltage (12-volt) or a low-voltage (VCC) program enable signal. The low voltage programming mode provides a convenient

33、 way to program the AT89C51 inside the users system, while the high-voltage programming mode is compatible with conventional third party Flash or EPROM programmers. The AT89C51 is shipped with either the high-voltage or low-voltage programming mode enabled. The respective top-side marking and device

34、 signature codes are listed in the following table.Vpp=12vVpp=5vTop-side markAT89C51xxxxyywwAT89C51xxxx-5yywwsignature(030H)=1EH(031H)=51H(032H)=FFH(030H)=1EH(031H)=51H(032H)=05HThe AT89C51 code memory array is programmed byte-bybyte in either programming mode. To program any nonblank byte in the on

35、-chip 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 progr

36、am 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 combination of control signals.4. Raise EA/VPP to 12V for the high-voltage programming mode.5. Pulse ALE/PROG once to progra

37、m a byte in the Flash array or the lock bits. The byte-write cycle is self-timed and typically takes no more than 1.5 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 ind

38、icate the end of a write cycle. During a write cycle, an attempted read of the last byte written will result in the complement of the written datum on PO.7. Once the write cycle has been completed, true data are valid on all outputs, and the next cycle may begin. Data Polling may begin any time afte

39、r a write cycle has been initiated.Ready/Busy: The progress of byte programming can also be monitored by the RDY/BSY output signal. P3.4 is pulled low after ALE goes high during programming to indicate BUSY. P3.4 is pulled high again when programming is done to indicate READY.Program Verify: If lock

40、 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 Progra

41、mmable and Erasable Read Only Memory array is erased electrically by using the proper combination 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 re-programmed.Reading the Signa

42、ture Bytes: The signature bytes are read by the same procedure as a normal verification of locations 030H, 031H, and 032H, except that P3.6 and P3.7 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

43、indicates 12V programming(032H) = 05H indicates 5V programmingProgramming InterfaceEvery code byte in the Flash array can be written and the entire array can be erased by using the appropriate combination of control signals. The write operation cycle is selftimed and once initiated, will automatical

44、ly time itself to completion.精選文檔AT89C51的概況AT89C51是美國(guó)ATMEL公司生產(chǎn)的低電壓，高性能CMOS8位單片機(jī)，片內(nèi)含4Kbytes的快速可擦寫(xiě)的只讀程序存儲(chǔ)器（PEROM）和128 bytes的隨機(jī)存取數(shù)據(jù)存儲(chǔ)器（RAM），器件接受ATMEL公司的高密度、非易失性存儲(chǔ)技術(shù)生產(chǎn)，兼容標(biāo)準(zhǔn)MCS-51產(chǎn)品指令系統(tǒng)，片內(nèi)置通用8位中心處理器（CPU）和flish存儲(chǔ)單元，功能強(qiáng)大AT89C51單片機(jī)可為您供應(yīng)很多高性?xún)r(jià)比的應(yīng)用場(chǎng)合，可機(jī)敏應(yīng)用于各種把握領(lǐng)域。主要性能參數(shù)：與MCS-51產(chǎn)品指令系統(tǒng)完全兼容4K字節(jié)可重復(fù)寫(xiě)flash閃速存儲(chǔ)器1000次

45、擦寫(xiě)周期全靜態(tài)操作：0HZ24MHZ三級(jí)加密程序存儲(chǔ)器128*8字節(jié)內(nèi)部RAM32個(gè)可編程I/O口2個(gè)16位定時(shí)計(jì)數(shù)器6個(gè)中斷源可編程串行UART通道低功耗空閑和掉電模式功能特性概述AT89C51供應(yīng)以下標(biāo)準(zhǔn)功能：4K 字節(jié)flish閃速存儲(chǔ)器，128字節(jié)內(nèi)部RAM，32個(gè)I/O口線，兩個(gè)16位定時(shí)計(jì)數(shù)器，一個(gè)5向量?jī)杉?jí)中斷結(jié)構(gòu)，一個(gè)全雙工串行通信口，片內(nèi)振蕩器準(zhǔn)時(shí)鐘電路。同時(shí)，AT89C51可降至0HZ的靜態(tài)規(guī)律操作，并支持兩種軟件可選的節(jié)電工作模式?？臻e方式停止CPU的工作，但允許RAM，定時(shí)計(jì)數(shù)器，串行通信口及中斷系統(tǒng)連續(xù)工作。掉電方式保存RAM中的內(nèi)容，但振蕩器停止工作并禁止其它全部部

46、件工作直到下一個(gè)硬件復(fù)位。引腳功能說(shuō)明Vcc：電源電壓GND：地P0口：P0口是一組8位漏極開(kāi)路型雙向I/O口，也即地址/數(shù)據(jù)總線復(fù)位口。作為輸出口用時(shí)，每位能吸取電流的方式驅(qū)動(dòng)8個(gè)規(guī)律門(mén)電路，對(duì)端口寫(xiě)“1”可 作為高阻抗輸入端用。 在訪問(wèn)外部數(shù)據(jù)存儲(chǔ)器或程序存儲(chǔ)器時(shí)，這組口線分時(shí)轉(zhuǎn)換地址（低8位）和數(shù)據(jù)總線復(fù)用，在訪問(wèn)期間激活內(nèi)部上拉電阻。P1口：P1是一個(gè)帶內(nèi)部上拉電阻的8位雙向I/O口，P1的輸出緩沖級(jí)可驅(qū)動(dòng)（吸取或輸出電流）4個(gè)TTL規(guī)律門(mén)電路。對(duì)端口寫(xiě)“1”，通過(guò)內(nèi)部的上拉電阻把端口拉到高電平，此時(shí)可做熟出口。做輸出口使用時(shí)，由于內(nèi)部存在上拉電阻，某個(gè)引腳被外部信號(hào)拉低時(shí)會(huì)輸出一個(gè)電

47、流（Iil）.Flash編程和程序校驗(yàn)期間，P1接受低8位地址。P2口：P2是一個(gè)帶有內(nèi)部上拉電阻的8位雙向I/O口，P2的輸出緩沖級(jí)可驅(qū)動(dòng)（吸取或輸出電流）4個(gè)TTL規(guī)律門(mén)電路。對(duì)端口寫(xiě)“1”，通過(guò)內(nèi)部地山拉電阻把端口拉到高電平，此時(shí)可作為輸出口，作輸出口使用時(shí)，由于內(nèi)部存在上拉電阻，某個(gè)引腳被外部信號(hào)拉低時(shí)會(huì)輸出一個(gè)電流（Iil）。在訪問(wèn)外部程序存儲(chǔ)器獲16位地址的外部數(shù)據(jù)存儲(chǔ)器（例如執(zhí)行 MOVX DPTR指令）時(shí)，P2口送出高8位地址數(shù)據(jù)。在訪問(wèn)8位地址的外部數(shù)據(jù)存儲(chǔ)器（如執(zhí)行 MOVX RI指令）時(shí)，P2口線上的內(nèi)容（也即特殊功能寄存器（SFR）區(qū)中R2寄存器的內(nèi)容），在整個(gè)訪問(wèn)期間

48、不轉(zhuǎn)變。Flash編程或校驗(yàn)時(shí)，P2亦接受高地址和其它把握信號(hào)。P3口：P3口是一組帶有內(nèi)部上拉電阻的8位雙向I/O口。P3口輸出緩沖級(jí)可驅(qū)動(dòng)（吸取或輸出電流）4個(gè)TTL規(guī)律門(mén)電路。對(duì)P3口寫(xiě)入“1”時(shí)，他們被內(nèi)部上拉電阻拉高并可作為輸出口。做輸出端時(shí)，被外部拉低的P3口將用上拉電阻輸出電流（Iil）。P3口除了作為一般的I/O口線外，更重要的用途是它的其次功能，如下表所示：端口引腳其次功能P3.0rxd (串行輸入口)P3.1txd (串行輸出口)P3.2int0 (外中斷0)P3.3int1 (外中斷1)P3.4t0 (定時(shí)/計(jì)數(shù)器0)P3.5t1 (定時(shí)/計(jì)數(shù)器1)P3.6 WR (外部

49、數(shù)據(jù)存儲(chǔ)器寫(xiě)選通)P3.7RD (外部數(shù)據(jù)存儲(chǔ)器讀選通)P3口還接收一些用于flash閃速存儲(chǔ)器編程和程序校驗(yàn)的把握信號(hào)。RST：復(fù)位輸入。當(dāng)振蕩器工作時(shí)，RST引腳消滅兩個(gè)機(jī)器周期以上高電平將使單片機(jī)復(fù)位。ALE/PROG：當(dāng)訪問(wèn)外部程序存儲(chǔ)器或數(shù)據(jù)存儲(chǔ)器時(shí)，ALE（地址所存允許）輸出脈沖用于所存地址的低8位字節(jié)。即使不訪問(wèn)外部存儲(chǔ)器，ALE仍以時(shí)鐘振蕩頻率的1/6輸出固定的正脈沖信號(hào)，因此它可對(duì)外輸出時(shí)鐘或用于定時(shí)目的。要留意的是：每當(dāng)訪問(wèn)外部數(shù)據(jù)存儲(chǔ)器時(shí)將跳過(guò)一個(gè)ALE脈沖。對(duì)flash存儲(chǔ)器編程期間，該引腳還用于輸入編程脈沖（PROG）。如有不要，可通過(guò)對(duì)特殊功能寄存器（SFR）區(qū)中的

50、8EH單元的D0位置位，可禁止ALE操作。該外置位后，只要一條MOVX和MOVC指令A(yù)LE才會(huì)被激活。此外，該引腳會(huì)被微弱拉高，單片機(jī)執(zhí)行外部程序時(shí)，應(yīng)設(shè)置ALE無(wú)效。PSEN：程序存儲(chǔ)允許（PSEN）輸出是外部程序存儲(chǔ)器的讀選通信號(hào)，當(dāng)AT89C51由外部程序存儲(chǔ)器取指令（或數(shù)據(jù)）時(shí)，每個(gè)機(jī)器周期兩個(gè)PSEN有效，即輸出兩個(gè)脈沖。在此期間，當(dāng)訪問(wèn)外部數(shù)據(jù)存儲(chǔ)器，這兩次有效的PSEN信號(hào)不消滅。EA/VPP:外部訪問(wèn)允許。欲使CPU僅訪問(wèn)外部程序存儲(chǔ)器（地址為0000H-FFFFH），EA端必需保持低電平（接地）。需留意的是; 假如加密位LB1被編程，復(fù)位時(shí)內(nèi)部會(huì)鎖存EA端狀態(tài)。如 EA端為高

51、電平（接VCC端），CPU則執(zhí)行內(nèi)部程序存儲(chǔ)器中的指令。Flash存儲(chǔ)器編程時(shí)，該引腳加上+12V的編程允許電源VPP，當(dāng)然這必需是該器件是使用12V編程電壓VPP.XTAL1: 振蕩器反相放大器的及內(nèi)部時(shí)鐘發(fā)生器的輸出端。XTAL2: 振蕩器反相放大器的輸出端。時(shí)鐘振蕩器：AT89C51中有一個(gè)用于構(gòu)成內(nèi)部振蕩器的高增益反相放大器，引腳XTAL1和XTAL2分別是該放大器的輸入端和輸出端。這個(gè)放大器與作為反饋的片外石英晶體或陶瓷諧振器一起構(gòu)成自激振蕩器，振蕩電路參見(jiàn)圖5。外接石英晶體（或陶瓷諧振器）及電容C1、C2接在放大器的反饋回路中構(gòu)成并聯(lián)振蕩電路。對(duì)外接電容C1、C2雖然沒(méi)有格外嚴(yán)格的

52、要求，但電容容量的大小會(huì)稍微影響振蕩頻率的凹凸、振蕩器的穩(wěn)定性、起振的難易程度及溫度穩(wěn)定性，假如使用石英晶體，我們推舉電容使用30PF+10PF，而如使用陶瓷諧振器建議選擇40PF+10PF。用戶(hù)也可以接受外部時(shí)鐘。接受外部時(shí)鐘的電路如圖5右所示。這種狀況下，外部時(shí)鐘脈沖接到XTAL1端，即內(nèi)部時(shí)鐘發(fā)生器的輸入端，XTAL2則懸空由于外部時(shí)鐘信號(hào)是通過(guò)一個(gè)2分頻觸發(fā)器后作為內(nèi)部時(shí)鐘信號(hào)的，所以對(duì)外部時(shí)鐘信號(hào)的占空比沒(méi)有特殊要求，但最小高電平持續(xù)時(shí)間和最大的低電平持續(xù)時(shí)間應(yīng)符合產(chǎn)品技術(shù)要求?？臻e模式：在空閑工作模式狀態(tài)，CPU保持睡眠狀態(tài)而全部片內(nèi)的外設(shè)仍保持激活狀態(tài)，這種方式由軟件產(chǎn)生。此時(shí)，

53、片內(nèi)RAM和全部特殊功能寄存器的內(nèi)容保持不變?？臻e模式可由任何允許的中斷懇求或硬件復(fù)位終止。終止空閑工作模式的方法有兩種，其一是任何一條被允許中斷的大事被激活，即可終止空閑工作模式。程序會(huì)首先響應(yīng)中斷，進(jìn)入中斷服務(wù)程序，執(zhí)行完中斷服務(wù)程序并僅隨終端返回指令，下一條要執(zhí)行的指令就是使單片機(jī)進(jìn)入空閑模式那條指令后面的一條指令。其二是通過(guò)硬件復(fù)位也可將空閑工作模式終止，需要留意的是，當(dāng)由硬件復(fù)位來(lái)終止空閑模式時(shí)，CPU通常是從激活空閑模式那條指令的下一條指令開(kāi)頭連續(xù)執(zhí)行程序的，要完成內(nèi)部復(fù)位操作，硬件復(fù)位脈沖要保持兩個(gè)機(jī)器周期（24個(gè)時(shí)鐘周期）有效，在這種狀況下，內(nèi)部禁止CPU訪問(wèn)片內(nèi)RAM，而允許

54、訪問(wèn)其它端口。為了避開(kāi)可能對(duì)端口產(chǎn)生以外寫(xiě)入，激活空閑模式的那條指令后一條指令不應(yīng)當(dāng)是一條對(duì)端口或外部存儲(chǔ)器的寫(xiě)入指令。空閑和掉電模式外部引腳狀態(tài)模式程序存儲(chǔ)器ALEPSENPORT0 PORT1PORT2PORT3空閑模式內(nèi)部11數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)空閑模式外部11浮空數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)掉電模式內(nèi)部00數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)掉電模式外部00浮空數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)掉電模式在掉電模式下，震蕩器停止工作，進(jìn)入掉電模式的指令是最終一條被執(zhí)行的指令，片內(nèi)RAM和特殊功能寄存器的內(nèi)容在終止掉電模式前被凍結(jié)。退出掉電模式的唯一方法是硬件復(fù)位，復(fù)位后將重新定義全部特殊功能寄存器但不轉(zhuǎn)變RAM中的內(nèi)容，在VCC恢復(fù)到正常工作電平前

55、，復(fù)位應(yīng)無(wú)效，且必需保持肯定時(shí)間以使振蕩器重啟動(dòng)并穩(wěn)定工作。程序存儲(chǔ)器的加密 ：AT89C51可使用對(duì)芯片上的3個(gè)加密位進(jìn)行編程（P）或不編程（U）來(lái)得到如下表所示的功能：加密位愛(ài)護(hù)功能表程序加密位愛(ài)護(hù)類(lèi)型LB1 LB2LB31UUU沒(méi)有程序愛(ài)護(hù)功能2PUU禁止從外部程序存儲(chǔ)器中執(zhí)行MOVC指令讀取內(nèi)部程序存儲(chǔ)器的內(nèi)容3PPU除上表功能外，還禁止程序校驗(yàn)4PPP除以上功能外，同時(shí)禁止外部執(zhí)行當(dāng)加密位LB1被編程時(shí)，在復(fù)位期間，EA端的規(guī)律電平被采樣并鎖存，假如單片機(jī)上電后始終沒(méi)有復(fù)位，則鎖存起的初始值是一個(gè)隨機(jī)數(shù)，且這個(gè)隨機(jī)數(shù)會(huì)始終保持到真正復(fù)位為止。為使單片機(jī)能正常工作，被鎖存的EA電平值必

56、需與該引腳當(dāng)前的規(guī)律電平全都。此外，加密位只能通過(guò)整片擦除的方法清除。FLASH閃速存儲(chǔ)器的編程：AT89C51單片機(jī)內(nèi)部有4K字節(jié)的FLASH PEROM,這個(gè)FLASH存儲(chǔ)陣列出廠時(shí)已處于擦除狀態(tài)（即全部存儲(chǔ)單元的內(nèi)容均為FFH），用戶(hù)隨時(shí)可對(duì)其進(jìn)行編程。編程接口可接收高電平（+12V）或低電平（VCC）的允許編程信號(hào)，低電平編程模式適合于用戶(hù)再線編程系統(tǒng)，而高電平編程模式可與通用EPROM編程器兼容。AT89C51單片機(jī)中，有些屬于低電壓編程方式，而有些則是高電平編程方式，用戶(hù)可從芯片上的型號(hào)和讀取芯片內(nèi)的簽名字節(jié)獲得該信息，見(jiàn)下表。Vpp=12vVpp=5v芯片頂面標(biāo)識(shí)AT89C51x

57、xxxyywwAT89C51xxxx-5yyww簽名字節(jié)(030H)=1EH(031H)=51H(032H)=FFH(030H)=1EH(031H)=51H(032H)=05HAT89C51的程序存儲(chǔ)器陣列是接受字節(jié)寫(xiě)入方式編程的，每次寫(xiě)入一個(gè)字節(jié)，要對(duì)整個(gè)芯片內(nèi)的PEROM程序存儲(chǔ)器寫(xiě)入一個(gè)非空字節(jié)，必需使用片擦除的方式將整個(gè)存儲(chǔ)器的內(nèi)容清除。編程方法：編程前，需按表1、圖3和圖4所示設(shè)置好地址，數(shù)據(jù)及把握信號(hào)， AT89C51編程方法如下：1.在地址線上加上要編程單元的地址信號(hào)。2.在數(shù)據(jù)線上加上要寫(xiě)入的數(shù)據(jù)字節(jié)。3.激活相應(yīng)的把握信號(hào)。4.在高電壓編程方式時(shí)，將EA/VPP端加上+12V編程電壓。5.每對(duì)FLASH存儲(chǔ)陣列寫(xiě)入一個(gè)字節(jié)或每寫(xiě)入一個(gè)程序加密位，加上一個(gè)ALE/PROG編程脈沖，轉(zhuǎn)變編程單元的地址和寫(xiě)入的數(shù)據(jù)，重復(fù)15步驟，直到全部文件編程結(jié)束。每個(gè)字節(jié)寫(xiě)入周期是自身定時(shí)地，通常約為1.5ms。數(shù)據(jù)查