Hi All,
I made rs232 to rs485 and rs485 to rs232 to communicate between 2 computers.This is the schematic that i wire it in breabboard:
and this is my program to test:
This schematic is only for test.I used only one computer to test, thus i tied TX of comm port to 232 input of max232 and RX like schematic.The problem is is that when i USED ground pin of comm port and tied to negative of 5V voltage supply, I received data exactly what I sent but When I not connected GND of comm port then I supprise when I received EVEN 5V voltage supply is not connected.BUt if GND of comm port is not used I only received if 5V voltage supply is not connected.Could you explain me why this happen?What should I do?And is there any wrong in this schematic?Thanks.
I made rs232 to rs485 and rs485 to rs232 to communicate between 2 computers.This is the schematic that i wire it in breabboard:
and this is my program to test:
Rich (BB code):
#include <cstdlib>
#include <iostream>
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <string.h>
#define TIMEOUT_CONSTANT 50
#define ESC 27
int main(int argc, char* argv[])
{
char*s="rs232 to rs485 converter";
int key_pressed = 0,i=0;
char outchar = 0;
char inchar = 0;
DWORD bytes_written = 0; // Number of bytes written to port
DWORD bytes_read = 0; // Number of bytes read from port
COMMTIMEOUTS tempComTimeouts; // Our temporary time-outs for COM1
COMMTIMEOUTS savedComTimeouts; // Stores the original time-outs
HANDLE comport = NULL; // Handle for COM port
DCB comSettings; // Contains various port settings
char buf[25];
printf("com port communication");
printf("COM1 program\n\n");
// Open COM port
if ((comport =
CreateFile("COM1",
GENERIC_READ | GENERIC_WRITE, // for reading and writing
0, // exclusive access
NULL, // no security attributes
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
NULL)) == INVALID_HANDLE_VALUE)
{
printf("Unable to open COM1.\n\n");
printf("Press any key to exit.");
getch();
return(1);
}
printf("COM1 opened.\n\n");
// Save time-out parameters for COM1
GetCommTimeouts(comport,&savedComTimeouts);
// Set our time-outs
tempComTimeouts.ReadIntervalTimeout = TIMEOUT_CONSTANT;
tempComTimeouts.ReadTotalTimeoutMultiplier = TIMEOUT_CONSTANT;
tempComTimeouts.ReadTotalTimeoutConstant = TIMEOUT_CONSTANT;
tempComTimeouts.WriteTotalTimeoutMultiplier = TIMEOUT_CONSTANT;
tempComTimeouts.WriteTotalTimeoutConstant = TIMEOUT_CONSTANT;
SetCommTimeouts(comport,&tempComTimeouts);
// Set Port parameters.
// We make a call to GetCommState() first in order to fill
// the comSettings structure with all the necessary values.
// Then we change the ones we want and call SetCommState().
GetCommState(comport, &comSettings);
comSettings.BaudRate = CBR_9600;
comSettings.StopBits = ONESTOPBIT;
comSettings.ByteSize = 8;
comSettings.Parity = NOPARITY;
comSettings.fParity = FALSE;
SetCommState(comport, &comSettings);
while(1)
{
i=0;
while(s!=0)
{
// Send data. if succesful, WriteFile() returns non-zero
WriteFile(comport, // Handle
&s, // Outgoing data
1, // Number of bytes to write
&bytes_written, // Number of bytes written
NULL); i++;
}
// Read data. if succesful, ReadFile() returns non-zero
ReadFile(comport, // Handle
buf, // Incoming data
sizeof(buf), // Number of bytes to read
&bytes_read, // Number of bytes read
NULL);
DWORD j;
printf("\n%s", buf);
for(i=0;i<25;i++)
buf='\0';
}
// Restore time-out parameters
SetCommTimeouts(comport,&savedComTimeouts);
CloseHandle(comport);
getch();
return(0);
}
This schematic is only for test.I used only one computer to test, thus i tied TX of comm port to 232 input of max232 and RX like schematic.The problem is is that when i USED ground pin of comm port and tied to negative of 5V voltage supply, I received data exactly what I sent but When I not connected GND of comm port then I supprise when I received EVEN 5V voltage supply is not connected.BUt if GND of comm port is not used I only received if 5V voltage supply is not connected.Could you explain me why this happen?What should I do?And is there any wrong in this schematic?Thanks.
