51 Single chip microcomputer learning notes "Six"--serial communication experiment

I. Serial communication Fundamentals 1. Serial communication

• Serial traffic divides the data bytes into one-bit form and transmits them one at a transmission line. Single-chip microcomputer adopts serial communication. Features are: Less transmission lines, low long-distance transmission costs, but data transmission control complex.
• Transmission direction of serial communication: simplex (data transmission can only be carried in one direction), run duplex (transmit data and accept data distribution), full duplex (transmission and accept synchronous).
• MCU uses asynchronous communication, sending and receiving devices using their own clock frequency, easy to achieve, but the transmission efficiency is not high, data format
  

2.max232

• The experiment can convert the serial port level ( -12V~+12V) of the computer to single chip and TTL level by MAX232 level conversion chip. Circuit schematic diagram is as follows
  

3.80c51 Serial Port

Write data to the send buffer sbuf, two physically independent receive, send buffer sbuf, they occupy the same address 99H, the receiver is a double buffer structure, send buffer, because the CPU is active when sending, does not produce overlapping errors.

4. Working Mode Register Scon

bit	D7	D6	D5	D4	D3	D2	D1	D0
Function	SM0	SM1	SM2	REN	TB8	RB8	T1	R1

• Introduced
• RI: Receive interrupt flag bit
  At the end of the reception, 1 of the hardware is placed, and the interrupt request is made to the CPU. (To be reset by software)
• TI: Send interrupt flag bit
  At the end of the send, the hardware is set to 1 and an interrupt request is made to the CPU. To be reset by software)
• TB8: Used to store the 9th bit of the send.
• RB8: Used to store the received 9th bit.
• REN: is a serial receive allow bit
  0 o'clock: Allow serial reception
  1 o'clock: Serial reception is not allowed

5. Working Mode Register Pcon

• The Pcon is not bit addressable, that is, it cannot directly manipulate the Smod to operate the Pcon register directly.
• Smod: Is the baud rate double the selection bit.
  0 o'clock: Baud rate does not double.
  1 o'clock: Double the baud rate.

6. Serial port operation step: First step: Set baud rate, set timer T1 to work Mode 2 (set Tmod Register), give counter initial value (mode 2 will reload automatically) Second step: Set the serial port working mode, set the Scon (if allowed). The third step: if the interrupt mode is used, then the corresponding interrupts and total interrupts are turned on. Fourth step: Turn on the timer T1 and start generating the baud rate. Tcon Set TRX. Two. Experimental routine 1. Description: This experiment uses the serial debugging assistant to send data to the computer, and returns, the experiment does not need the wiring. 2. The program source code is as follows:

/************************************** > File Name: Serial communication experiment > AUTHOR:PENGSHP > Mail: [email protected] & Gt date:2015 July 22 ***************************************/#include <reg51.h>#define UCHAR unsigned char#define UINT unsigned intUchar Flag,i;/ * Serial initialization function * /voidInit_uart () {scon=0x50;//Set to working mode 1Tmod=0x20;//Set how the counter works 2pcon=0x80;//baud rate doubledth1=0xf3;//Counter initial value, baud rate is 4800tl1=0xf3; Ea=1;//Open Total Interruptes=1;//Open Accept interrupttr1=1;//Turn on the counter}voidMain () {Init_uart (); while(1)    {if(flag==1) {es=0;//Shut down serial interruptflag=0; Sbuf=i;//Received data written to Sbuf             while(! TI);//Decide whether to send outTi=0; es=1;//Open serial interrupt}     }}voidSerial () interrupt4{ri=0;//Accept the flag-clear 0I=sbuf;//Read data from Sbufflag=1;//instructions to receive data}

Baud rate calculation and operation of the introduction of a small, commonly used baud rate of 9600, crystal oscillator frequency of 11.0592MHZ, the error is 0%. I use a crystal oscillator frequency of 12MHZ, there is a certain error.

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

51 Single chip microcomputer learning note "Six"--serial communication experiment