【正文】 s 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, 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).4. In intelligent instruments on the application Singlechip microputer with small size, low power consumption, control function is strong, flexible, miniaturization and extended use of convenience etc, widely used in instrumentation, bined with different kinds of sensors, such as voltage, power can be realized, the frequency, the humidity, temperature and flow rate, speed, thickness, Angle, length, hardness, elements, pressure measurements of physical quantities. Adopting SCM control makes instrumentation digital, intelligent, miniaturization, and function by electronic or digital circuit than more powerful. For example precision measurement equipment (power meter, oscilloscope, various analyzer).2. The application in industrial control Using SCM can make various control systems, data acquisition system. For example factory assembly line of intelligent tube operand that participate in the operation or operand address is located (that is, the operand stored in the local code). Because the single chip is a programmable device, only recognize the binary code (0,1). Operation to singlechip, singlechip microputer system in all directions, must be the form of binary code to represent. For example, in Intel39。 fourth step: End the sum of the results to the specified memory unit. All of these take a number, send a few, the sum of deposit, etc. are a few operations (Operation), we asked the puter to operate with the implementation of the various forms of writing down the order, which is instruction. But how can we identify them and to perform these operations? This is a single chip in the design by the designers of the instruction given to it by decision. A mand, corresponding to a basic operation。 Secondly, there must be able to pla