① 需要一篇自動控制方面的英文文獻
本畢業設計課題是屬於教師擬定性課題，主要是研究基於單片機的對步進電機的有效控制。步進電機是一種能將數字輸入脈沖轉換成旋轉舉察或直線增量運動的電磁執行元件，每輸入蠢虛一個脈沖電機轉軸步進一個步距角增量。電機總的回轉角與輸入脈沖數成正比例，相應的轉速取決於輸入脈沖頻率。
步進電機是機正檔茄電一體化產品中關鍵部件之一，通常被用作定位控制和定速控制。步進電機慣量低、定位精度高、無累積誤差、控制簡單等特點。廣泛應用於機電一體化產品中，如：數控機床、包裝機械、計算機外圍設備、復印機、傳真機等。
Abstract
This article mainly elaborated has been hanging the movement control system merit, introced was hanging the movement control system function, the principle and the design process. Is hanging the movement control system is one of in control engineering domain important applications, its main target is to is controlled the object the movement condition, including path, speed and position implementation check. The movement control system compares with other control systems, has the system model simply, the check algorithm is unitary, also not complex characteristic and so on non-linearity and coupling situation. Also is precisely because the movement control system can implement to the path, the running rate, the pointing accuracy as well as the repetition precision accuracy control requirement, has the broad application foreground in each category of control engineering, therefore the movement control system has at present become in the check study application domain very much significant the research direction. Through the monolithic integrated circuit to stepping monitor check, implemented the motor-driven to cause the object at on the board which inclined the movement, The control section is the SST89E52 monolithic microcomputer which SST Corporation proces primarily, with when the 1602LCD liquid crystal screen and according to turned has implemented with the user interactive, through the keyboard entry different control command, the liquid-crystal display was allowed to display the setting value and the run the coordinates. The electrical machinery control section used LM324N four to transport puts and is connected the electronic primary device voluntarily to develop the 42BYG205 stepping monitor actuation electric circuit to implement the electrical machinery accuracy control. The algorithm partially for will suit the monolithic integrated circuit system to operate carries on optimizes many times, will rece the microprocessor the operand. Has completed the object voluntarily the movement and according to the different setup path movement.
Key words Magneto; 1602LCD; LM324N; Drive circuit
選擇步進電機時，首先要保證步進電機的輸出功率大於負載所需的功率。而在選用功率步進電機時，首先要計算機械繫統的負載轉矩，電機的矩頻特性能滿足機械負載並有一定的餘量保證其運行可靠。在實際工作過程中，各種頻率下的負載力矩必須在矩頻特性曲線的范圍內。一般地說最大靜力矩Mjmax大的電機，負載力矩大[1 ]。
選擇步進電機時，應使步距角和機械繫統匹配，這樣可以得到機床所需的脈沖當量。在機械傳動過程中為了使得有更小的脈沖當量，一是可以改變絲桿的導程，二是可以通過步進電機的細分驅動來完成。但細分只能改變其解析度，不改變其精度。精度是由電機的固有特性所決定。
選擇功率步進電機時，應當估算機械負載的負載慣量和機床要求的啟動頻率，使之與步進電機的慣性頻率特性相匹配還有一定的餘量，使之最高速連續工作頻率能滿足機床快速移動的需要。
基於單片機的懸掛運動控制系統，具有硬體電路結構簡單，精確度高，抗干擾性強等優點。
1.2 課題目的
培養綜合運用四年大學所學知識去分析問題和解決實際問題的能力。在實踐中檢驗所學知識,從而加強理論與實踐的相結合。 體驗一個科研項目開發的全過程，學會單片機開發應用方法,鍛煉應用能力,動手能力。本課題設計是具有一定難度的基於單片機的應用系統開發項目，培養學生創新精神和創新能力。通過這次畢業論文及設計，檢驗的綜合素質和專業教育的培養效果，並且使學會閱讀、利用英文文獻資料，閱讀並翻譯外文資料的能力，學會設計報告和論文。
1.3 課題意義
隨著社會的發展、科技的進步以及人們生活水平的逐步提高，各種方便於生活的自動控制系統開始進入了人們的生活，以單片機為核心的自動門系統就是其中之一。同時也標志了自動控制領域成為了數字化時代的一員[ 3]。它實用性強，功能齊全，技術先進，使人們相信這是科技進步的成果。它更讓人類懂得，數字時代的發展將改變人類的生活，將加快科學技術的發展。
通過對「微機控制自動門系統」的研究和設計，精心撰寫了微機控制自動門系統論文。本論文著重闡述了以單片機為主體，LED點陣顯示晶元及步進電機為核心的系統。
本設計主要應用SST89E58作為控制核心，LED點陣顯示晶元、步進電機、壓力感測器、電位器相結合的系統。充分發揮了單片機的性能。其優點硬體電路簡單，軟體功能完善，控制系統可靠，性價比較高等特點，具有一定的使用和參考價值。
1.4 應解決的主要問題
在基於單片機的懸掛運動控制系統中，主要分三個部分設計，一個是輸入和鍵盤顯示模塊；另一個是步進電機驅動模塊；第三個是最小系統和輸出模塊設計。主要解決的問題是：
1. 單片機最小系統硬體設計；
2. 步進電機驅動模塊設計；
3. 輸出部分的軟硬體設計；
4. 主程序設計；
5. 繪圖板的設計。
1.5 技術要求
設計一電機控制系統，控制物體在傾斜（仰角≤100度）的板上運動。
在一白色底板上固定兩個滑輪，兩只電機（固定在板上）通過穿過滑輪的吊繩控制一物體在板上運動，運動范圍為80cm×100cm。物體的形狀不限，質量大於100克。物體上固定有淺色畫筆，以便運動時能在板上畫出運動軌跡。板上標有間距為1cm的淺色坐標線（不同於畫筆顏色），左下角為直角坐標原點。
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② 關於單片機方面的英文文獻，最還有翻譯
基於單片機的電子表設計
摘要：近年來隨著計算機在社會領域的滲透和大規模集成電路的發展，單片機的應用正在不斷地走向深入，由於它具有功能強，體積小，功耗低，價格便宜，工作可靠，使用方便等特點，因此特別適合於與控制有關的系統，越來越廣泛地應用於自動控制，智能化儀器，儀表，數據採集，軍工產品以及家用電器等各個領域，單片機往往是作為一個核心部件來使用，在根據具體硬體結構，以及針對具體應用對象特點的軟體結合，以作完善。
本次做的電子表是以單片機（AT89S51）為核心，結合相關的元器件（共陰極LED數碼顯示器、BCD-鎖存/7段解碼等），再配以相應的軟體，達到實現時鍾日歷顯示的功能，也具有日歷計算、顯示和時鍾、日歷的校準，以及多路開關定時輸出等功能，其硬體部分難點在於元器件的選擇、布局及焊接。
Based on the design of electronic SCM
Abstract: In recent years, with computer penetration in the social sphere and the development of large-scale integrated circuits, MCU applications are constantly deepening, as it has a function of strong, small size, low power consumption, cheap, reliable, Easy to use, and other characteristics, and therefore particularly suited to control the system, more widely used in automatic control, intelligent instruments, meters, data acquisition, military procts and household appliances, and other fields, the MCU is often as a core Parts to use, in accordance with specific hardware and application-specific characteristics of the object with software to make perfect.
This is done in electronic form SCM (AT89S51) as the core, the combination of related components (of cathode LED digital display, BCD-latch / 7 of the decoder, and so on), Coupled with the corresponding software, to achieve Clock calendar shows that the function of the calendar also calculated, display and the clock, the calendar of calibration, and multi-channel Kaiguandingshi output, and other functions, some of its hardware components is difficult choice, layout and welding.
③ 求：有關MCS-51單片機的英文文獻
MCS-51單片機指令系統集（英文注釋）
原先帖子（內容相同）的被鎖定了！各位，不好意思啊！麻煩宋老師把原先的開掉！
MCS-51指令系統集（英文注釋）
若帖子中若有疏漏或謬誤之處，敬請及時批評指正，以免誤導真正「新手上路」的年輕小蝦們！
按功能分為五大類：
（1）數據傳送類指令（7種助記符）
MOV（英文為Move）：對內部數據寄存器RAM和特殊功能寄存器SFR的數據進行傳送；
MOVC（Move Code）讀取程序存儲器數據表格的數據傳送；
MOVX (Move External RAM) 對外部RAM的數據傳送；
XCH (Exchange) 位元組交換；
XCHD (Exchange low-order Digit) 低半位元組交換；
PUSH (Push onto Stack) 入棧；
POP (Pop from Stack) 出棧；
（2）算術運算類指令（8種助記符）
ADD(Addition) 加法；
ADDC(Add with Carry) 帶進位加法；
SUBB(Subtract with Borrow) 帶借位減法；
DA(Decimal Adjust) 十進制調整；
INC(Increment) 加1；
DEC(Decrement) 減1；
MUL(Multiplication、Multiply) 乘法；
DIV(Division、Divide) 除法；
(3)邏輯運算類指令（10種助記符）
ANL(AND Logic) 邏輯與；
ORL(OR Logic) 邏輯或；
XRL(Exclusive-OR Logic) 邏輯異或；
CLR(Clear) 清零；
CPL(Complement) 取反；
RL(Rotate left) 循環左移；
RLC(Rotate Left throught the Carry flag) 帶進位循環左移；
RR(Rotate Right) 循環右移；
RRC (Rotate Right throught the Carry flag) 帶進位循環右移；
SWAP (Swap) 低4位與高4位交換；
(4)控制轉移類指令（17種助記符）
ACALL（Absolute subroutine Call）子程序絕對調用；
LCALL（Long subroutine Call）子程序長調用；
RET（Return from subroutine）子程序返回；
RETI（Return from Interruption）中斷返回；
SJMP（Short Jump）短轉移；
AJMP（Absolute Jump）絕對轉移；
LJMP（Long Jump）長轉移；
CJNE (Compare Jump if Not Equal)比較不相等則轉移；
DJNZ (Decrement Jump if Not Zero)減1後不為0則轉移；
JZ (Jump if Zero)結果為0則轉移；
JNZ (Jump if Not Zero) 結果不為0則轉移；
JC (Jump if the Carry flag is set)有進位則轉移；
JNC (Jump if Not Carry)無進位則轉移；
JB (Jump if the Bit is set)位為1則轉移；
JNB (Jump if the Bit is Not set) 位為0則轉移；
JBC(Jump if the Bit is set and Clear the bit) 位為1則轉移，並清除該位；
NOP (No Operation) 空操作；
（5）位操作指令（1種助記符）
SETB(Set Bit) 位 置1 。
下次抽空將各條指令的用法，用我自己地話（個人的理解），再來「牛」一下，以供參考。同時，我也很希望各位大蝦，多「出版」一些高質量的好東東（包括學習心得），最好系統些。給像我這樣的班門弄斧的小蝦，做做榜樣，引引路，好讓真正「新手上路」的單片機愛好者少走彎路，我想，這時我們單片機初學者共同的心聲！所謂愚者千慮，必有一得，我們小蝦們，在學習中發現的東東多往上帖帖，就當作是練習吧！
互相協作！
④ 求單片機參考文獻，中文的有相應的外文翻譯
[1]楊十元.模擬系統故障診斷與可靠性設計，清華人學出版社，2004
[2]童詩白.模擬電子技術基礎，高教出版社，2006
[3]周航慈.單片機應用程序設計技術，北京航空航大大學出版社，2005
[4]李剛.ADuC812系列單片機原理和應用技術，北京航空航天山版社，2005
[5]胡誕康.在線測試技術的發展與展望，計量與測試技術，2001
[6]星河科技開發公司，印刷電路板在線測試系統的發展與應用，電子標准化與測量，2003
[7]季華.PCB測試技術的綜合利用，電子產品世界，2007-12
[8]鮮壇.組裝測試技術應用前景分析，世界電子元器件，2008-1
[9]張金敏.基於單片機控制的智能電阻電容在線測試儀，甘肅科技，2006
[10]庄紹雄王濟浩張迎春.智能阻容在線測試技術，山東工業大學學報，
[11]陳國順陳春沙王格芳等.通用電路板在線測試儀設計與開發，儀器儀表學報，2001
[12]Nancy Hplland.Automated Instruments Smooth Rapid Test System Development.Test & Measurement World,AUGUST 2001
[13]盧育強.如何設定ICT的上下限，電子生產設備，2003 142-143
[14]趙悅 沈青松 終玉軍.路板的測試技術，遼寧工學院學報，2008-1
[15]程亞黎 曾周末.電路故障自動測試與診斷系統，中國儀器儀表，2007
⑤ 大哥你幫我也整一篇關於單片機的英文文獻~3000字的 還要有中文翻譯~謝謝了
1. About SCM
It can be said across the twentieth century, the three "electric" era, that is, electrical era, the electronic age, and has now entered the computer age. However, such a computer, usually refers to the personal computer, referred to as PC. It consists of the host, keyboard, monitor etc.. Another type of computer, most people do not know how. This computer is to smart to give a variety of mechanical microcontroller (also known as micro-controller). As the name suggests, this computer system only used the smallest one IC, you can perform simple operations and control. Because of its small size, usually hidden in a charged mechanical "stomach" Lane. It is the entire device, like the human brain plays a role, it goes wrong, the whole device was paralyzed.
Now, this MCU has a very wide field of use, such as smart meters, real-time instrial control, communications equipment, navigation systems, home appliances and so on. Once the microcontroller were using a variety of procts, you can serve to upgrade the effectiveness of the proct, often in the proct name is preceded by the adjective - "smart", such as washing machines and so intelligent. At present, some technical personnel of factories or other amateur electronics developers to engage in out of certain procts, not the circuit is too complex, that is, functions are too simple and easy to be copied. The reason may be stuck in the proct without the use of a microcontroller or other programmable logic device.
SCM basic component is a central processing unit (CPU in the computing device and controller), read-only memory (usually expressed as a ROM), read-write memory (also known as Random Access Memory MRAM is usually expressed as a RAM) , input / output port (also divided into parallel port and serial port, expressed as I / O port), and so composed. In fact there is also a clock circuit microcontroller, so that ring operation and control of the microcontroller, can rhythmic manner. In addition, there are so-called "break system", the system is a "janitor" role, when the microcontroller control object parameters that need to be intervention to reach a particular state, can after this "janitor" communicated to the CPU, so that CPU priorities of the external events to take appropriate counter-measures.
單片機的簡介
可以說，二十世紀跨越了三個「電」的時代，即電氣時代、電子時代和現已進入的電腦時代。不過，這種電腦，通常是指個人計算機，簡稱PC機。它由主機、鍵盤、顯示器等組成。還有一類計算機，大多數人卻不怎麼熟悉。這種計算機就是把智能賦予各種機械的單片機（亦稱微控制器）。顧名思義，這種計算機的最小系統只用了一片集成電路，即可進行簡單運算和控制。因為它體積小，通常都藏在被控機械的「肚子」里。它在整個裝置中，起著有如人類頭腦的作用，它出了毛病，整個裝置就癱瘓了。
現在，這種單片機的使用領域已十分廣泛，如智能儀表、實時工控、通訊設備、導航系統、家用電器等。各種產品一旦用上了單片機，就能起到使產品升級換代的功效，常在產品名稱前冠以形容詞——「智能型」，如智能型洗衣機等。現在有些工廠的技術人員或其它業余電子開發者搞出來的某些產品，不是電路太復雜，就是功能太簡單且極易被仿製。究其原因，可能就卡在產品未使用單片機或其它可編程邏輯器件上。
單片機的基本組成是由中央處理器（即CPU中的運算器和控制器）、只讀存貯器（通常表示為ROM）、讀寫存貯器（又稱隨機存貯器通常表示為RAM）、輸入/輸出口（又分為並行口和串列口，表示為I/O口）等等組成。實際上單片機裡面還有一個時鍾電路，使單片機在進行運算和控制時，都能有節奏地進行。另外，還有所謂的「中斷系統」，這個系統有「傳達室」的作用，當單片機控制對象的參數到達某個需要加以干預的狀態時，就可經此「傳達室」通報給CPU，使CPU根據外部事態的輕重緩急來採取適當的應付措施。
⑥ 單片機英文文獻及翻譯，5000字左右 急需 謝謝 [email protected]
Introction of Programmable controllers
From a simple heritage, these remarkable systems have evolved to not only replace electromechanical devices, but to solve an ever-increasing array of control problems in both process and nonprocess instries. By all indications, these microprocessor powered giants will continue to break new ground in the automated factory into the 1990s.
HISTORY
In the 1960s, electromechanical devices were the order of the day ass far as control was concerned. These devices, commonly known as relays, were being used by the thousands to control many sequential-type manufacturing processes and stand-along machines. Many of these relays were in use in the transportation instry, more specifically, the automotive instry. These relays used hundreds of wires and their interconnections to effect a control solution. The performance of a relay was basically reliable - at least as a single device. But the common applications for relay panels called for 300 to 500 or more relays, and the reliability and maintenance issues associated with supporting these panels became a very great challenge. Cost became another issue, for in spite of the low cost of the relay itself, the installed cost of the panel could be quite high. The total cost including purchased parts, wiring, and installation labor, could range from $30~$50 per relay. To make matters worse, the constantly changing needs of a process called for recurring modifications of a control panel. With relays, this was a costly prospect, as it was accomplished by a major rewiring effort on the panel. In addition these changes were sometimes poorly documented, causing a second-shift maintenance nightmare months later. In light of this, it was not uncommon to discard an entire control panel in favor of a new one with the appropriate components wired in a manner suited for the new process. Add to this the unpredictable, and potentially high, cost of maintaining these systems as on high-volume motor vehicle proction lines, and it became clear that something was needed to improve the control process – to make it more reliable, easier to troubleshoot, and more adaptable to changing control needs.
That something, in the late 1960s, was the first programmable controller. This first 『revolutionary』 system wan developed as a specific response to the needs of the major automotive manufacturers in the United States. These early controllers, or programmable logic controllers (PLC), represented the first systems that 1 could be used on the factory floor, 2 could have there 『logic』 changed without extensive rewiring or component changes, and 3 were easy to diagnose and repair when problems occurred.
It is interesting to observe the progress that has been made in the past 15 years in the programmable controller area. The pioneer procts of the late 1960s must have been confusing and frightening to a great number of people. For example, what happened to the hardwired and electromechanical devices that maintenance personnel were used to repairing with hand tools? They were replaced with 『computers』 disguised as electronics designed to replace relays. Even the programming tools were designed to appear as relay equivalent presentations. We have the opportunity now to examine the promise, in retrospect, that the programmable controller brought to manufacturing.
All programmable controllers consist of the basic functional blocks shown in Fig. 10. 1. We』ll examine each block to understand the relationship to the control system. First we look at the center, as it is the heart ( or at least the brain ) of the system. It consists of a microprocessor, logic memory for the storage of the actual control logic, storage or variable memory for use with data that will ordinarily change as a function power for the processor and memory. Next comes the I/O block. This function takes the control level signals for the CPU and converts them to voltage and current levels suitable for connection with factory grade sensors and actuators. The I/O type can range from digital (discrete or on / off), analog (continuously variable), or a variety of special purpose 『smart』 I/O which are dedicated to a certain application task. The programmer is shown here, but it is normally used only to initially configure and program a system and is not required for the system to operate. It is also used in troubleshooting a system, and can prove to be a valuable tool in pinpointing the exact cause of a problem. The field devices shown here represent the various sensors and actuators connected to the I/O. These are the arms, legs, eyes, and ears of the system, including push buttons, limit switches, proximity switches, photosensors, thermocouples, RTDS, position sensing devices, and bar code reader as input; and pilot lights, display devices, motor starters, DC and AC drives, solenoids, and printers as outputs.
No single attempt could cover its rapidly changing scope, but three basic characteristics can be examined to give classify an instrial control device as a programmable controller.
(1) Its basic internal operation is to solve logic from the beginning of memory to some specified point, such as end of memory or end of program. Once the end is reached, the operation begins again at the beginning of memory. This scanning process continues from the time power is supplied to the time it it removed.
(2) The programming logic is a form of a relay ladder diagram. Normally open, normally closed contacts, and relay coils are used within a format utilizing a left and a right vertical rail. Power flow (symbolic positive electron flow) is used to determine which coil or outputs are energized or deenergized.
(3) The machine is designed for the instrial environment from its basic concept; this protection is not added at a later date. The instrial environment includes unreliable AC power, high temperatures (0 to 60 degree Celsius), extremes of humidity, vibrations, RF noise, and other similar parameters.
General application areas
The programmable controller is used in a wide variety of control applications today, many of which were not economically possible just a few years ago. This is true for two general reasons: 1 there cost effectiveness (that is, the cost per I/O point) has improved dramatically with the falling prices of microprocessors and related components, and 2 the ability of the controller to solve complex computation and communication tasks has made it possible to use it where a dedicated computer was previously used.
Applications for programmable controllers can be categorized in a number of different ways, including general and instrial application categories. But it is important to understand the framework in which controllers are presently understood and used so that the full scope of present and future evolution can be examined. It is through the power of applications that controllers can be seen in their full light. Instrial applications include many in both discrete manufacturing and process instries. Automotive instry applications, the genesis of the programmable controller, continue to provide the largest base of opportunity. Other instries, such as food processing and utilities, provide current development opportunities.
There are five general application areas in which programmable controllers are used. A typical installation will use one or more of these integrated to the control system problem. The five general areas are explained briefly below.
Description
The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes of Flash programmable and erasable read only memory (PEROM). The device is manufactured using Atmel』s high-density nonvolatile memory technology and is compatible with the instry-standard MCS-51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining 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.
Function characteristic
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 plex serial port, on-chip oscillator and clock circuitry. In addition, 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 contents but freezes the oscillator disabling all other chip functions until the next hardware reset.
Pin Description
VCC：Supply voltage.
GND：Ground.
Port 0：
Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as highimpedance inputs.Port 0 may also be configured to be the multiplexed loworder address/data bus ring accesses to external program and data memory. In this mode P0 has internal pullups.Port 0 also receives the code bytes ring Flash programming,and outputs the code bytes ring programverification. External pullups are required ring programverification.
Port 1
Port 1 is an 8-bit bi-directional I/O port with internal pullups.The Port 1 output buffers can sink/source four TTL inputs.When 1s are written to Port 1 pins they are pulled high by the internal pullups 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 pullups.Port 1 also receives the low-order address bytes ring Flash programming and verification.
Port 2
Port 2 is an 8-bit bi-directional I/O port with internal pullups.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 pullups and can be used as inputs. As inputs,Port 2 pins that are externally being pulled low will source current, because of the internal pullups.Port 2 emits the high-order address byte ring fetches from external program memory and ring accesses to external data memory that use 16-bit addresses. In this application, it uses strong internal pullupswhen emitting 1s. During accesses to external data memory that use 8-bit addresses, Port 2 emits the contents of the P2 Special Function Register.Port 2 also receives the high-order address bits and some control signals ring Flash programming and verification.
Port 3
Port 3 is an 8-bit bi-directional I/O port with internal pullups.The 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 pullups and can be used as inputs. As inputs,Port 3 pins that are externally being pulled low will source current (IIL) because of the pullups.Port 3 also serves the functions of various special features of the AT89C51 as listed below:
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 the low byte of the address ring accesses to external memory. This pin is also the program pulse input (PROG) ring 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, that one ALE pulse is skipped ring 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 ring a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no 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 ring each access 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 is programmed, EA will be internally latched on reset.EA should be strapped to VCC for internal program executions.This pin also receives the 12-volt programming enable voltage(VPP) ring Flash programming, for parts that require12-volt VPP.
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating 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 be 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 ty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be observed.
Figure 1. Oscillator Connections Figure 2. External Clock Drive Configuration
Idle Mode
In idle mode, the CPU puts itself to sleep while all the onchip peripherals remain active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain unchanged ring 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 algorithm 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 that writes to a port pin or to external memory.
Power-down Mode
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 redefines 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 Bits
On the chip are three lock bits which can be left unprogrammed (U) or can be programmed (P) to obtain the additional features listed in the table below.
When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched ring reset. If the device 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