【正文】 , has a special expertise in its services unit, that is, the stack pointer SP, whenever a PUSH instruction execution, SP on (in the Based on the original value) automatically add 1, whenever the implementation of a POP instruction, SP will (on the basis of the original value) automatically by 1. As the SP values can be changed with the instructions, so long as the beginning of the process to change the value of the SP, you can set the stack memory unit required, such as the program begins, with an MOV SP, 5FH instructions When set on the stack starting from the memory unit 60H unit. There is always the beginning of the general procedure with such a directive to set the stack pointer, because boot, SP initial value of 07H, 08H This unit from the beginning to stack next, and 08H to 1FH 8031 is the second in the region, three or four working register area, often used, this will lead to confusion of data. Different authors when writing programs, initialize the stack is not exactly the same directive, which is the author39。and39。, and the stack has a special data transmission instructions that39。unit must be stored in a single instruction. 5, the stack: Stack is a region, is used to store data, there is no special about the region itself is a part of internal RAM, special access to its data storage and the way that the socalled 39。 units started, that is: the system must exist in ROM 0000 39。s implementation:Reduction in power after the 8051 microcontroller within the program counter (PC) in the value of 0000 39。 as a generalpurpose I / O port to use. You can arrange the order of a SETB 39。 but (user) 39。 is also not a 39。 form the sequence. In other words, addresses, instructions are also data. Instruction: from single chip designer provides a number of monly used instructions with mnemonic we have a strict correspondence between the developer can not be changed by the MCU. Address: the search for MCU internal, external storage units, input and output port based on the address of the internal unit value provided by the chip designer is good, can not be changed, the external unit can be single chip developers to decide, but there are a number of address units is a must (see procedures for the implementation of the process). Third, P0 port, P2 and P3 of the second function I use: Beginners often on the P0 port, P2 and P3 port I use the second function puzzled that the second function and have a switch between the original function of the process, or have a directive, in fact, the port The second feature is automatic, do not need instructions to convert. Such as , respectively WR, RD signal, when the microchip processing machines external RAM or external I / O port, they are used as a second function, not as a generalpurpose I / O port used, so long as a A microprocessor implementation of the MOVX instruction, there will be a corresponding signal sent from the or , no prior use of mands. In fact 39。and 39。s data connection is known as the data bus, the device is called line of control all the control bus. Internal or external memory in the microcontroller and other devices have memory cells, the memory cell to be assigned addresses, you can use, distribution, of course, to address given in the form of electrical signals, and as more memory cells, so, for the address allocation The line is also more of these lines is called the address bus.Second, data, address, mandThe reason why these three together because of the nature of these three are the same the number, or are a string of 39。s responsibility inevitably falls on electrical, electronics manufacturers. From this point of view, Intel faded MCU development has its objective factors. In the development of MCU, the most famous manufacturers as the number of Philips Corporation. Philips pany in embedded applications, its great advantage, the MCS51 singlechip microputer from the rapid development of the microcontroller. Therefore, when we look back at the path of development of embedded systems, do not forget Intel and Philips in History. Embedded SystemsEmbedded system microcontroller is an independent development path, the MCU important factor in the development stage, is seeking applications to maximize the solution on the chip。s with a series of successful SCM market, the result will be a drastic change! Just because you are prepared by microputer programs can achieve high intelligence, high efficiency and high reliability!As the microcontroller on the costsensitive, so now the dominant software or the lowest level assembly language, which is the lowest level in addition to more than binary machine code language, and as so low why is the use? Many highlevel language has reached the level of visual programming Why is not it? The reason is simply that there is no ho