Generation of C51HEX file and single-chip minimum system

Figure 2-2 Project Options Window

Figure 2-3 Compile Information Window

Perhaps you have burned the compiled file to the chip. If you buy or make a learning experiment board with serial port output components, you can connect the serial port to the PC serial port and use the serial port debugging software or Windows HyperTerminal to set the baud rate to 1200, and you can see the words "Hello World!" being output continuously. If you don't have an experiment board yet, let's talk about the AT89c51 minimum system first, and then use an example program to verify whether the minimum system is running. This minimum system is also easy to make for experiments. Figure 2-4 is the AT89c51 minimum system. However, in order to let us see that it is running, a resistor and an LED are added to display its status. The crystal oscillator can be used according to your own situation. Generally, 11.0592MHz or 12MHz is used on the experiment board. The advantage of using the former is that it can generate a standard serial port baud rate, while the latter has a machine cycle of 1 microsecond, which is convenient for precise timing. In my own experiments, please note that VCC is +5V, which cannot be higher than this value, otherwise the microcontroller will be damaged. If it is too low, it will not work properly. Pin 31 must be connected to a high level so that we can execute the program in the chip. If it is connected to a low level, the program memory outside the chip will be used. Let's create a new project named OneLED to verify whether the minimized system can work. The program is as follows:

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#include //Preprocessing command

void main(void) //main function name

{

//This is the first comment method

unsigned int a; //define variable a as int type

/* This is the second comment type

*/

do{ //do while loop

for (a=0; a<50000; a++); //This is a loop P1_0 = 0; //Set P1.0 port to low level and turn on the LED for (a=0; a<50000; a++); //This is a loop P1_0 = 1; //Set P1.0 port to high level and turn off the LED

}

while(1);

}

Figure 2-4 AT89c51 Minimized System

Here we will first talk about the comment statements supported by the KEIL C compiler. One is the statement that starts with the "//" symbol. The statements after the symbol are considered comments until there is a carriage return. The other is the comment within the "/*" and "*/" symbols. Comments will not be compiled by the C compiler. A C application program should have a main function, which can call other functions.

function, but other function are not allowed to call main function. No matter where the main function is placed in the program, it is always executed first. Use the knowledge learned above to compile the OneLED program and burn it into the newly made minimized system. Power on, the LED is not bright at first (because all IO ports are set to 1 pins at high level after power-on reset), then delay for a period of time (for (a=0; a<50000; a++) is running), the LED is bright, and then delay again, the LED goes out, and then alternately lights up and goes out. The first real small experiment is done. If there is no such effect, then you should carefully check the circuit or the steps of compiling and burning.