Implementation of Serial Communication between LabVIEW and STC89C54 MCU

　　1. Overview

　　In modern measurement and control systems, we often use the development and control mode of the host computer and the slave computer. The slave computer is mainly used to collect data, which can be realized through embedded controllers, single-chip microcomputer controllers, PLCs, etc. The host computer is mainly a graphical interface, which is used to display the collected data in real time, analyze and process the data, and control the slave computer at the same time. The host computer can be realized through various high-level languages, such as VB, Delphi, etc., as well as NI's graphical virtual instrument software development environment LabVIEW. Since LabVIEW uses a graphical programming method, whether you have programming experience or not, you can quickly and efficiently design the user interface, realize communication with the control hardware, and perform data analysis and processing. Today, LabVIEW has penetrated into various fields of industrial measurement, and at the same time it also plays a huge role in embedded, FPGA, DSP, real-time control and other fields.

　　2. Functions implemented in this example

　　First, use the microcontroller STC89C54 to send "Hello, LabVIEW" through the serial port, and LabVIEW will send the microcontroller to the data for display. Through this example, you can understand the serial communication design of LabVIEW.

　　3. Hardware design and software design of the lower computer

　　(1) Hardware design

　　The hardware circuit design of the microcontroller serial port communication is relatively simple, mainly including the microcontroller STC89C54 minimum system, MAX232 and a nine-pin serial port.

　　(2) Software Design

　　The design source code is as follows:

　　#include

　　#define uchar unsigned char

　　#define uint unsigned int

　　void SendStr(unsigned char *s); //send

　　String

　　void DelayMs (uint xms) //delay sub-function

　　{

　　uint i,j;

　　for（i=xms;i>0;i-）

　　for(j=110;j>0;j-);

　　}

　　void InitUART（void） //Serial port initialization

　　{

　　SCON=0×50; //SCON: mode

　　1,8-bitUART,receive enabled

　　TMOD|=0×20; //TMOD:timer 1,mode

　　2,8-bit reinstall

　　TH1=0xFD; // TH1: reload value 9600 waves

　　Crystal Oscillator: 11.0592MHz

　　TR1=1; //TR1: timer 1 is turned on

　　EA=1; //Open the general interrupt

　　}

　　void main(void)

　　{

　　initUART();

　　while(1)

　　{

　　SendStr("Hello! LabVIEW!");

　　DelayMs(240);

　　DelayMs(240);

　　}

　　}

　　void SendByte(unsigned char dat)

　　{

　　SBUF=dat;

　　while(!TI);

　　TI=0;

　　}

　　void SendStr(unsigned char *s)

　　{

　　while（*s!=\'\\0'）//\\0 indicates the end of the string

　　Flag, // detect whether the string ends

　　{

　　SendByte(*s);

　　s++;

　　}[page]

　　4. Host computer LabVIEW front panel and program flowchart

　　(1) Introduction to related functions

　　When doing LabVIEW serial communication, you must first install the VISA driver, which can be downloaded from the Internet. LabVIEW's operations on the serial port are mainly read and write operations. This example mainly receives data, that is, read operations. Here we first introduce the controls and functions related to this example.

　　①VISA resource name

　　Under the "New" control tab, under the "I/O" sub-tab, there is a "VISA Resource Name" control. After installing the VISA driver and connecting to the hardware, the corresponding COM ports can be listed under this control, and you can select the appropriate COM port.

　　②VISA configures the serial port function

　　This function is located in the "Instrument I/O"

　　The sub-tabs are mainly used to configure the serial port parameters, including baud rate, data bits, parity check, etc.

　　③VISA read and VISA close functions

　　The VISA Read function reads a specified number of bytes from the device or interface specified by the VISA resource name and returns the data to the read buffer. The VISA Close function closes the device session handle or event object specified by the VISA resource name.

　　(2) Program flowchart design

　　The program flowchart design is shown in Figure 1.

　　5. Testing

　　After connecting the hardware, power on, download the program, and run labVIEW, we can see that the string "Hello! LavVIEW" sent by the microcontroller is received in the read buffer, as shown in Figure 2.

　　6. Summary

　　The host computer is designed using LabVIEW, which has a beautiful interface and is easy to implement. It can be easily used in various measurement and monitoring systems.