【正文】 as shown in Schedule 1. Third, special function register Special Function Register (SFR) address the range of 80H ~ FFH. In the MCS51, in addition to program counter register PC and four work areas, and the remaining 21 special function register SFR in this block. Of which five are doublebyte register, which takes up a total of 26 bytes. The special function registers and address of the symbols see Table 2. Which can be with * bit addressable. Special Function Registers 8051 reflects the state of the state of 8051 is actually the word and control word register. CPU PSW is typical for a case. Special Function Registers in general these two categories, with the pin on the chip, and the other for chip control function. With the chip on the pin is the Special Function Registers P0 ~ P3, they are in fact four of eight latches (one for each I / O port A), each additional latch corresponding output driver and input buffer constitutes a parallel port. MCS51 a total of four such P0 ~ P3 the parallel port provides 32 I / O lines, each line is a twoway, and has the second largest function. The rest used for chip control register, the accumulator A, marks register PSW, the data pointer DPTR function mentioned before, while others function registers part of the back of the further introduction Singlechip instruction and addressing mode To the normal operation of singlechip, to be programmed in advance, and then the procedure Add memory, and then from the CPU to implement the program. Procedure is posed by the directive, Directive is an essential ponent of the operation code and operands. Many varieties of singlechip, the design of how that operation code and operands, have their own requirements, and then there are instructions code varies, therefore, must be singlechip all the selected mand, which is the socalled instruction sufficient understanding. Although the various series of singlechip systems have different mands, but also has its monality. Instructions have a singlechip system, for other series of singlechip can play a role prehend by analogy. MCS51 singlechip applications, derived varieties, representative, therefore, here to MCS51 series as an example of the mand system mand the position and , MOV A, 20H The instructions said to 20H into the accumulator A of the number of (a special function register). 譯文： 單片機(jī)的組成 單片機(jī)要自動完成計(jì)算，它應(yīng)該具有哪些最重要的部分呢？ 我們以打算盤為例計(jì)算一道算術(shù)題。 34. Now to carry out operations, first of all need a plan, followed by Pen and paper. We have to calculate the issue of record, and then count the first step, 163 156, add it with the results of 36 recorded in the paper, and then calculate 166 247。 single chip can implement all the mands, the mand is the singlechip system (Iustruction Set), different types of singlechip, and its mand system is also different. The use of singlechip, the prior should be the problem to be solved into a series of mands. These instructions must be selected to identify and implement singlechip instructions. Singlechip customers to solve their own problems by the instructions for the procedure, known as source code (Source Program). Usually divided into opcode instruction (Opcode) and operand (Operand) of two major parts. Operation of the puter code that the implementation of any operation, that is, the function of mand。 34，再把它從上一次結(jié)果中減去，就得到最后的結(jié)果。這種對輸入、輸出數(shù)據(jù)進(jìn)行一定管理的“門”電路在單片機(jī)中稱為“口”（ Port）。顧名思義，只讀存貯器一旦將數(shù)據(jù)存入，就只能讀出，不能更改（ EPROM、 E2PROM 等類型的 ROM 可通過一定的方法來更改、寫入數(shù)據(jù) —— 編者注）。另外，還有所謂的“中斷系統(tǒng)”，這個(gè)系統(tǒng)有“傳達(dá)室”的作用，當(dāng)單片機(jī)控制對象的參數(shù)到達(dá)某個(gè)需要加以干預(yù)的狀態(tài)時(shí)，就可經(jīng)此“傳達(dá)室”通報(bào)給 CPU，使 CPU 根據(jù)外部事態(tài)的輕重緩急來采取適當(dāng)?shù)膽?yīng)付措施。只有將各種正確的程序“灌入”（存入 ）單片機(jī)，它才能有效地工作。這些指令必須是選定的單片機(jī)能識別和執(zhí)行的指令。 MCS－ 51 單片機(jī)的字長為 8 位，有時(shí)，要完成某 些操作用一個(gè)字節(jié)尚不能充分表達(dá)。匯編可借助于人工查表法來實(shí)現(xiàn)，也可借助 PC 機(jī)通過所謂“交叉匯編程序”來完成。其每位的具體含意如下所示。 MCS－ 51 反映帶符號數(shù)的運(yùn)算結(jié)果是否有溢出，有溢出時(shí)，此位為 1，否則為 0。要單片機(jī)執(zhí)行一個(gè)程序，就必須把該程序按順序預(yù)先裝入存儲器 ROM 的某個(gè)區(qū)域。存儲器中每個(gè)存儲單元可存放一個(gè)八位二進(jìn)制信息，通常用兩位 16 進(jìn)制數(shù)來表示，這就是存儲器的內(nèi)容。不過，這時(shí)應(yīng)使 8051 的第 {31}腳（即 EA 腳）保持低電平。而用做特殊功能寄存器的地址為 80H～ FFH。其中 5 個(gè)是雙字節(jié)寄存器，它們共占用了 26個(gè)字節(jié)。其余用于芯片 控制的寄存器中，累加器 A、標(biāo)志寄存器 PSW、數(shù)據(jù)指針 DPTR 等的功能前已提及，而另一些寄存器的功能在后面有關(guān)部分再作進(jìn)一步介紹 單片機(jī)的指令系統(tǒng)和尋址方式 單片機(jī)要正常運(yùn)作，事先需編制程序，再把程序放入存貯器中，然后由 CPU執(zhí)行該程序。