【文章內(nèi)容簡介】 onchip RAM and Special Function Registers retain their values until the powerdown mode is terminated. The only exit from powerdown is a hardware reset. Reset redefines the SFRS but does not change the onchip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize. The AT89C51 code memory array is programmed byteby byte in either programming mode. To program any nonblank byte in the onchip Flash Memory, the entire memory must be erased using the Chip Erase Mode. 2 Programming Algorithm Before programming the AT89C51, the address, data and control signals should be set up according to the Flash programming mode table and Figure 3 and Figure 4. To program the AT89C51, take the following . Input the desired memory location on the address . Input the appropriate data byte on the data lines. 3. Activate the correct bination of control signals. 4. Raise EA/VPP to 12V for the highvoltage programming mode. 5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The bytewrite cycle is selftimed and typically takes no 安徽理工大學畢業(yè)設(shè)計外文文獻翻譯 6 more than ms. Repeat steps 1 through 5, changing the address and data for the entire array or until the end of the object file is reached. Data Polling: The AT89C51 features Data Polling to indicate the end of a write cycle. During a write cycle, an attempted read of the last byte written will result in the plement of the written datum on . Once the write cycle has been pleted, true data are valid on all outputs, and the next cycle may begin. Data Polling may begin any time after a write cycle has been initiated. : The progress of byte programming can also be monitored by the RDY/BSY output signal. is pulled low after ALE goes high during programming to indicate BUSY. is pulled high again when programming is done to indicate READY. Program Verify: If lock bits LB1 and LB2 have not been programmed, the programmed code data can be read back via the address and data lines for verification. The lock bits cannot be verified directly. Verification of the lock bits is achieved by observing that their features are enabled. Chip Erase: The entire Flash array is erased electrically by using the proper bination of control signals and by holding ALE/PROG low for 10 ms. The code array is written with all “ 1” s. The chip erase operation must be executed before the code memory can be reprogrammed. Reading the Signature Bytes: The signature bytes are read by the same procedure as a normal verification of locations 030H, 031H, and 032H, except that and must be pulled to a logic low. The values returned areas follows. (030H) = 1EH indicates manufactured by Atmel (031H) = 51H indicates 89C51 (032H) = FFH indicates 12V programming (032H) = 05H indicates 5V programming Programming Interface Every code byte in the Flash array can be written and the entire array can be erased by using the appropriate bination of control signals. The write operation 安徽理工大學畢業(yè)設(shè)計外文文獻翻譯 7 cycle is self timed and once initiated, will automatically time itself to pletion. A microputer interface converts information between two forms. Outside the microputer the information handled by an electronic system exists as a physical signal, but within the program, it is represented numerically. The function of any interface can be broken down into a number of operations which modify the data in some way, so that the process of conversion between the external and internal forms is carried out in a number of steps. An analogtodigital converter(ADC) is used to convert a continuously variable signal to a corresponding digital form which can take any one of a fixed number of possible binary values. If the output of the transducer does not vary continuously, no ADC is necessary. In this case the signal conditioning section must convert the ining signal to a form which can be connected directly to the next part of the interface, the input/output section of the microputer itself. Output interfaces take a similar form, the obvious difference being that here the flow of information is in the opposite direction。 it is passed from the program to the outside world. In this case the program may call an output subroutine which supervises the operation of the interface and performs the scaling numbers which may be needed for digitaltoanalog converter(DAC). This subroutine passes information in turn to an output device which produces a corresponding electrical signal, which could be converted into analog form using a DAC. Finally the signal is conditioned(usually amplified) to a form suitable for operating an actuator. The signals used within microputer circuits are almost always too small to be connected directly to the outside world” and some kind of interface must be used to translate them to a more appropriate form. The design of section of interface circuits is one of the most important tasks facing the engineer wishing to apply microputers. We have seen that in microputers information is represented as discrete patterns of bits。 this digital form is most useful when the microputer is to be connected to equipment which can only be switched on or off, where each bit might represent the state of a switch or actuator. To solve realworld problems, a microcontroller must have more than just a CPU, a program, and a data memory. In addition, it must contain hardware allowing the CPU to access information from the outside world. Once the CPU gathers information and processes the data, it must also be able to effect change on some portion o