【正文】 各個系列的單片機雖然有不同的指令系統(tǒng)，但也有其共同性。特殊功能寄存器反映了 8051 的狀態(tài)，實際上是 8051 的狀態(tài)字及控制字寄存器。從 00H 到 1FH 安排了四組工作寄存器，每組占用 8 個 RAM 字節(jié)，記為 R0～ R7。其最大容量可擴展到 64k，用于存儲實時輸入的數(shù)據(jù)。如前述用助記符編寫的命令 MOV A，＃ 20H，換成機器認識的代碼 74H、 20H：（寫成二進制就是 01110100B 和 00100000B）。當單片機開始執(zhí)行 程序時，給 PC 裝入第一條指令所在地址，它每取出一條指令（如為多字節(jié)指令，則每取出一個指令字節(jié)）， PC 的內(nèi)容就自動加 1，以指向下一條指令的地址，使指令能順序執(zhí)行。 PSW 的其它位，將在以后再介紹。它表示了運算是否有進位（或借位）。 一、運算器 運算器以完成二進制的算術 /邏輯運算部件 ALU 為核心，再加上暫存器 TMP、累加器 ACC、寄存器 B、程序狀態(tài)標志寄存器 PSW 及布爾處理器 。所以，直接用它來編寫程序十分困難。操作碼表示計算機執(zhí)行什么操作，即指令的功能；操作數(shù)表示參加操作的數(shù)或操作數(shù)所在的地址（即操作數(shù)所存放的地方編號）。 第二步：把第二個數(shù)從它所在的存貯單元中取出來，送至運算器； 第三步：相加； 第四步：把相加完的結果，送至 存貯器中指定的單元。從而，一切指令、數(shù)據(jù)都可經(jīng)內(nèi)部總線傳送，有如大城市內(nèi)各種物品的傳送都經(jīng)過干道進行 單片機指令系統(tǒng)與匯編語言程序 前面已經(jīng)講述了單片機的幾個主要組成部分，這些部分構成了單片機的硬件。單片機除了進行運算外，還要完成控制功能。這樣要由外部設備通過“口”進入單片機，再存放在存貯器中，在運算處理過程中，數(shù)據(jù)從存貯器讀入運算器進行運算，運算的中間結果要存入存貯器中，或最后由運算器經(jīng)“出入口”輸出。此外，還需要有能代替人作用的控制器，它能根據(jù)事先給定的命令發(fā)出各種控制信號，使整個計算過程能一步步地進行。s designated address, the corresponding unit from the ROM mand byte out of storage on the instruction register, and then, in the instruction register decoder instruction code has been translated into various forms of control signals, these signals with a single Machine clock oscillator clock pulse generated in the timing and control circuit in bination to form a certain period of time according to changes in level and beat the clock, the socalled control of information, internal coordination in the CPU data transfer between registers, and other puting operation. A program memory Control puter program is a series of action mands, singlechip only recognized by the 0 and 1 consisting of machine code instructions. Such as the preparation of the foregoing order by Mnemonic MOV A, 20H, understanding the code into the machine 74H, 20H: (written in binary is 01110100B and 00100000B). Deal with problems in the singlechip will be required before good procedures, tables, constants piled into machine code into the microcontroller memory, the memory as the program memory. Program memory can be put on the chip or chip, chipchip can also be set at the same time. As the PC program counter for 16bit, the program memory 16bit binary address can be used, therefore, the largest internal and external memory addresses from 0000H to FFFFH. 8051 there are 4k bytes of ROM, on the occupied by the 0000H ~ 0FFFH minimum 4k bytes, this chip to expand the program memory address 1000H numbers should be started, if you use 8051 as a 8031, do not want to use chip 4kROM , all bychip memory, the address number can be started by the 0000H. However, this should be the first 8051 feet (31) (that is, EA feet) remain low. When EA is high, the user 0FFFH in the range of 0000H to use the internal ROM, more than 0FFFH, the singlechip CPU access to external program memory automatically. Second, data storage Singlechip data memory RAM memory by reading and writing ponents. Its maximum capacity can be expanded to 64k, used to store realtime data input. 8051 there are 256 units of the internal data memory, in which 00H ~ 7FH for internal random access memory RAM, 80H ~ FFH register for the special zone. Actual use should be the first full use of internal memory, from the use of perspective, to understand the structure of internal data memory and address of the distribution is very important. Because the future directions in the study design of systems and procedures they will be frequently used. 8051 internal data memory address 00H to FFH by a total of 256 bytes of address space, the space was divided into two parts, of which the internal data RAM address 00H ~ 7FH (that is, 0 ~ 127). The Special Function Registers used as the address of 80H ~ FFH. 256 bytes in this also opened up a socalled digital address area, the region can not only byte addressing, but also by the bit (bit) addressable. For those who require databit operation can be stored to the region. From 00H to 1FH arranged the work of four groups of registers, each occupied by 8byte RAM, recorded as R0 ~ R7. Whether the choice of which set of registers, register by the aforementioned signs of RS1 and RS0 to choose. Add in the two different binary number, you can choose different groups of registers,