CODEWITHSUNDEEP
cwindowsuart
Ahmad Shah
Ahmad Shah

Reputation: 321

UART using C in Windows

I'm trying to establish a UART interface between an external Microcontroller and Windows using C.

I'm using the following code to set up the UART Parameters and then send in a character to the designated COM port.

I'm successful in sending a character. But How do I receive one back ? The code is as follows:

#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <math.h>
#include <string.h>

HANDLE hSerial;
int main()
{
// OPEN SERIAL PORT AND SET INITAL UART PARAMETERS 
//=================================================
DCB dcbSerialParams = {0}; COMMTIMEOUTS timeouts = {0};
fprintf(stderr, "Opening serial port...");
hSerial = CreateFile("\\\\.\\COM3", GENERIC_READ|GENERIC_WRITE, 0, NULL,OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL );

if (hSerial == INVALID_HANDLE_VALUE){fprintf(stderr, "Error\n");return 1;}
else {fprintf(stderr, "OK\n");}

// Set device parameters (115200 baud, 1 start bit, 1 stop bit, no parity)
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
if (GetCommState(hSerial, &dcbSerialParams) == 0){fprintf(stderr, "Error getting device state\n");CloseHandle(hSerial);return 1;}

dcbSerialParams.BaudRate = CBR_57600; dcbSerialParams.ByteSize = 8; dcbSerialParams.StopBits = ONESTOPBIT; dcbSerialParams.Parity = NOPARITY;

if(SetCommState(hSerial, &dcbSerialParams) == 0){fprintf(stderr, "Error setting device parameters\n");CloseHandle(hSerial);return 1;}

// Set COM port timeout settings
timeouts.ReadIntervalTimeout = 50; timeouts.ReadTotalTimeoutConstant = 50; timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50; timeouts.WriteTotalTimeoutMultiplier = 10;

if(SetCommTimeouts(hSerial, &timeouts) == 0){fprintf(stderr, "Error setting timeouts\n"); CloseHandle(hSerial); return 1;}



// SETUP AND SEND DATA FROM UART
//============================== 
    int VarNum=8;
    char str[15];
    sprintf(str,"%ld",VarNum);


    DWORD bytes_written, total_bytes_written = 0;
    fprintf(stderr, "Sending bytes...");
    if(!WriteFile(hSerial,str, strlen(str), &bytes_written, NULL))
    {
        fprintf(stderr, "Error\n");
        CloseHandle(hSerial);
        return 1;
    }   
    fprintf(stderr, "%d bytes written\n", bytes_written); 


// CLOSE SERIAL PORT AND EXIT MAIN FUNCTION
//=========================================
fprintf(stderr, "Closing serial port...");

if (CloseHandle(hSerial) == 0){fprintf(stderr, "Error\n"); return 1;}
fprintf(stderr, "OK\n");return 0;

}

Upvotes: 2

Views: 5549

Answers (1)

Danny_ds
Danny_ds

Reputation: 11406

You can use ReadFile() for that:

BOOL bOk = ReadFile(hSerial, buffer, sizeof(buffer) - 1, &bytesRead, NULL);
if (bOk && (bytesRead > 0)) {
    buffer[bytesRead] = '\0';
}

When reading from a serial port, ReadFile() should block until there is more data, or a timeout occurs. (this should be done in a seperate thread (in a loop), or maybe by using ReadFileEx() for asynchronous operation).

When reading from a communications device, the behavior of ReadFile is governed by the current communication time-outs as set and retrieved using the SetCommTimeouts and GetCommTimeouts functions. Unpredictable results can occur if you fail to set the time-out values.

Also checkout SetCommState() and PurgeComm().

Upvotes: 1

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