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RS232 & MAX232 serial communication

Iam connecting microcontroller 8051 with my PC COM1 port to have serial communication. To have same voltage levels between PC and 8051 i have used MAX232 but i need to know what other components like capacitors and resistor i need to connect in between controller and MAX232. i have the data sheet but information is limited.

so can any one suggest capacitor value and quanity and other minor components.

Parents

0 NORE NORE over 21 years ago in reply to Jon Ward

Hi Jon,

I have done one simple serial rs232 c program in keil and when download in eprom it produce no output on the termulator.This program is to do serial transmission from 8051 to pc.

Here is the code:

/* RS232 SIMPLE TRIAL */

#include <stdio.h>
#include <reg51.h>


/*Function to initialize RS232 serial port*/
void serial_init()
{
	SCON=0X50;		//Setup for 8-bit data
	TMOD=0X20;		//Setup Timer 1 for auto-reload
	TH1=0XFD;		//Setup for 9600 baud
	TR1=1;			//Turn on Timer 1
	T1=1;			//Indicate Ready to Transmit
}

/*This func display a null-terminated string on the rs232 port*/

void send_serial(unsigned char*s)
{
 while(*s!=0x0)
 {
  SBUF=*s;
  while(!T1)
  {  }
  T1=0;
  s++;
  }
}

/*Start of main program*/

main()
{
 unsigned char crlf[]={0x0D,0x0A,0x0};
 serial_init();
 for (;;)
 {
  send_serial("Another test");
  send_serial(crlf);
 }
}

since i am using off chip memory i have set it to 0x0000. But when i turn on the board, there is no data displayed except letter 'n'. Why this thing happen? I am using Maxim 232.

your help is much appreciated.

Reply

0 NORE NORE over 21 years ago in reply to Jon Ward

/* RS232 SIMPLE TRIAL */

#include <stdio.h>
#include <reg51.h>


/*Function to initialize RS232 serial port*/
void serial_init()
{
	SCON=0X50;		//Setup for 8-bit data
	TMOD=0X20;		//Setup Timer 1 for auto-reload
	TH1=0XFD;		//Setup for 9600 baud
	TR1=1;			//Turn on Timer 1
	T1=1;			//Indicate Ready to Transmit
}

/*This func display a null-terminated string on the rs232 port*/

void send_serial(unsigned char*s)
{
 while(*s!=0x0)
 {
  SBUF=*s;
  while(!T1)
  {  }
  T1=0;
  s++;
  }
}

/*Start of main program*/

main()
{
 unsigned char crlf[]={0x0D,0x0A,0x0};
 serial_init();
 for (;;)
 {
  send_serial("Another test");
  send_serial(crlf);
 }
}

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