【導(dǎo)讀】AT89S52是一種低功耗、高性能CMOS8位微控制器，具有8K在系統(tǒng)可編程Flash存儲器。使用Atmel公司高密度非易失性存儲器技術(shù)制造，與工業(yè)80C51產(chǎn)品指令和引腳完全兼容。片上Flash允許程序存儲器在系統(tǒng)可編程，亦適于常規(guī)編程器。在單芯片上，擁有靈巧的8位CPU和在系統(tǒng)可編程Flash，使得AT89S52為眾多嵌入式控制應(yīng)用系統(tǒng)提供高靈活、超有效的解決方案。AT89S52具有以下標(biāo)準(zhǔn)功能：8k字節(jié)Flash，256字節(jié)RAM，32位I/O口線，看門狗定時器，2個數(shù)據(jù)指針，三個16位定時器/計數(shù)器，一個6向量2級中斷結(jié)構(gòu)，全雙工串行口，片內(nèi)晶振及時鐘電路。另外，AT89S52可降至0Hz靜態(tài)邏輯操作，支持2種軟件可選擇節(jié)電模式。掉電保護(hù)方式下，RAM內(nèi)容被保存，振蕩器被凍結(jié)，單片機(jī)一切工作停止，直到下一個中斷或硬件復(fù)位為止。對P0端口寫“1”時，引腳用作高阻抗輸入。程序校驗(yàn)時，需要外部上拉電阻。這一位置“1”，ALE僅在執(zhí)行MOVX或MOVC指令時有效。定時器0和定時器1標(biāo)志位TF0和TF1在計數(shù)溢出的那個周期的S5P2被置位。

　　

【正文】 火花加工有許多優(yōu)點(diǎn)。 1 . 不論硬度高低，只要是導(dǎo)電材料都能對其進(jìn)行切削。對用常規(guī)方法極難切削的硬質(zhì)合金和超韌性的太空合金，電火化加工特別有價值。 2 . 工件可在淬火狀態(tài)下加工，因克服了由淬火引起的變形問題。 3 . 很容易將斷在工件中的絲錐和鉆頭除。 4 . 由于刀具（電極）從未與工件接觸過，故工件中不會產(chǎn)生應(yīng)力。 5 . 加工出的零件無毛刺。 6 . 薄而脆的工件很容易加工，且無毛刺。 Electrical discharge machiningElectrical discharge machining has proved especially valuable in the machining of supertough, electrically conductive materials such as the new spaceage alloys. These metals would have been difficult to machine by conventional methods, but EDM has made it relatively simple to machine intricate shapes that would be impossible to produce with conventional cutting tools. This machining process is continually finding further applications in the metalcutting industry. It is being used extensively in the plastic industry to produce cavities of almost any shape in the steel molds. Electrical discharge machining is a controlled metal removal technique whereby an electric spark is used to cut (erode) the workpiece, which takes a shape opposite to that of the cutting tool or electrode. The cutting tool (electrode) is made from electrically conductive material, usually carbon. The electrode, made to the shape of the cavity required, and the workpiece are both submerged in a dielectric fluid, which is generally a light lubricating oil. This dielectric fluid should be a nonconductor (or poor conductor) of electricity. A servo mechanism maintains a gap of about to in. ( to mm) between the electrode and the work, preventing them from ing into contact with each other. A direct current of low voltage and high amperage is delivered to the electrode at the rate of approximately 20 000 hertz (Hz). These electrical energy impulses bee sparks which jump the dielectric fluid. Intense heat is created in the localized area of the park impact, the metal melts and a small particle of molten metal is expelled from the surface of the workpiece . The dielectric fluid, which is constantly being circulated, carries away the eroded particles of metal and also assists in dissipating the heat caused by the spark.In the last few years, major advances have been made with regard to the surface finishes that can be produced. With the low metal removal rates, surface finishes of 2 to 4 um. ( to ) are possible. With high metal removal rates finishes of 1 000uin. (25um) are produced.The type of finish required determines the number of amperes which can be used, the capacitance, frequency, and the voltage setting. For fast metal removal (roughing cuts), high amperage, low frequency, high capacitance, and minimum gap voltage are required. For slow metal removal (finish cut) and good surface finish, low amperage, high frequency, low capacitance, and the highest gap voltage are required.Electrical discharge machining has many advantages over conventional machining processes.1. Any material that is electrically conductive can be cut, regardless of its hardness. It is especially valuable for cemented carbides and the new supertough spaceage alloys that are extremely difficult to cut by conventional means.2. Work can be machined in a hardened state, thereby overing the deformation caused by the hardening process.3. Broken taps or drills can readily be removed from workpieces. 4. It does not create stresses in the work material since the tool (electrode) never es in contact with the work.5. The process is burrfree.6. Thin, fragile sections can be easily machined without deforming.