Serial port asynchronous communication microcontroller programming example

org 0000H 

AJMP START 

ORG 30H 

START: 

mov SP,#5fh ; 

mov TMOD,#20h ;T1: work mode 2 

mov PCON,#80h ;SMOD=1 

mov TH1,#0FDH ;Initialize baud rate (see table) 

mov SCON,#50h ;Standard UART settings 

MOV R0,#0AAH ;Prepare to send data 

SETB REN ;Enable receiving 

SETB TR1 ;T1 starts working 

WAIT: 

MOV A,R0 

CPL A 

MOV R0,A 

MOV SBUF,A 

LCALL DELAY 

JBC TI,WAIT1 ;If TI is 1, clear TI and go to WAIT1 

AJMP WAIT 

WAIT1: JBC RI,READ ;If RI is 1, clear RI and go to READ 

AJMP WAIT1 

READ: 

MOV A,SBUF ;Send the obtained number to port P1 

MOV P1,A 

LJMP WAIT 

DELAY: ;Delay subroutine 

MOV R7,#0ffH 

DJNZ R7,$ 

RET 

END 

Compile the program, write it into the chip, insert it into the experimental board, and use the through-read cable to connect the experimental board to the serial port of the host to conduct the experiment. The function of the above program is very simple, which is to send 55H and AAH to the host in turn at regular intervals, and send the number sent by the host to port P1. You can use the serial port wizard on the PC to do experiments. The serial port wizard is available for download on my homepage. After running the serial port wizard, press the "Set Parameters" button on the main interface to enter the "Set Parameters" dialog box and set the parameters according to the following parameters. Note that my machine uses serial port 2. If you are not using serial port 2, please change the serial port settings yourself. 

After setting, press OK to return to the main interface. Note that there is a drop-down list on the right, and "According to Hexadecimal" should be selected. Then press "Start Sending" and "Start Receiving". According to this setting, two lights should be on and six lights should be off on the experimental board. You can change the sending characters in the setting parameters such as 55, 00, FF, etc., observe the lights on and off, and analyze the reasons. You can also change the "According to Hexadecimal" in the drop-down list on the main interface to "According to Decimal" or "According to ASCII Characters" to observe the phenomenon and analyze it carefully. This is also very helpful for everyone to understand hexadecimal, decimal, and ASCII characters. The program itself is very simple and has comments, so I won't explain it in detail here.