Library function printf in KeilC51

#include

#include /* Add to use printf function*/

main()

{

     SCON = 0x50; /*SCON: working mode 1, 8-bit UART, allow receiving*/

     TMOD |= 0x20;/*TMOD: Timer T1, working mode 2, 8-bit automatic reload mode*/

     TH1= 0xf3;/*When the baud rate is 2400, the timer initial value*/

     TR1= 1;/*Timer T1 starts running*/

     TI = 1; /*Allow sending data*/

     printf("hello world");

}

After debugging and running the above code, the serial port continuously outputs "hello world" and the program falls into an infinite loop.

Solution to the problem: add while(1); at the end of the program.

Reason: If you do not add while(1); the MCU will execute a RET instruction, which will reset the program.

           Bit (software reset, pop 0000H from the stack to the PC register), the program restarts after reset

           implement.

Thinking: I am used to programming in Windows. After the main program is executed, it will exit to the operating system, and the microcontroller will

           It’s different now, where to retreat? The following is the conversation between the microcontroller and the compiler:

           MCU: I have nothing to do, I'd rather die~~~

           Compiler: Want to die? You should reset it~~~RET

           MCU: o, shit~~~

MCU serial port related issues: The standard 51 has only one serial port, but now many MCUs based on the 51 core have

The microcontroller will have two or more serial ports, so which serial port does the printf function target?

Answer: There is a putchar.c file in the Keil\C51\LIB directory. The printf function will call the

The putchar function uses the standard 51 registers (such as TI, SBUF).

Their addresses are fixed, so we can see that the printf function only targets serial port 0.

Support serial port 1 or serial port 2. Then modify the register of putchar function, for example, change SBUF to

SBUF1. But can I use the printf function to apply to both serial port 0 and serial port 1? I want to do it myself.

French bar :)

In addition: If you just use printf to output a string, you should write a function yourself, because printf needs to process

The output of various types of data takes up a lot of code space. I tried it and there was only one printf statement in the program.

The code is 1K, and printf is also slow to execute.