Assuming you are using Windows, here is some basic Visual Studio C/C++ code that shows the Microsoft APIs needed to talk to the serial port hardware (virtual or real). COM2 would be replaced with the virtual com port used by mbed and in VS use the help feature to read about each API you don't understand. This is a simple console application (text only - no fancy GUI) and it just echos back what is read in until you type control C.
// SerialIO.cpp : Defines the entry point for the console application.
//
// Serial Port File I/O Demo Program
//
// FOR DEMO: Connect COM2: to PC with null modem cable
// 9600 Baud 8 data bits 1 stop bit
// no parity and no flow control
#include "stdafx.h"
BOOL ModifyCommSettings (HANDLE hComPort);
HANDLE hSerial;
int _tmain(int argc, TCHAR *argv[], TCHAR *envp[])
{
DWORD cBytes_out, cBytes_in;
DWORD dwMask;
char cBuffer_out[] = "\f\n Hello Serial World!\n\rType something and watch it echo back\n\rCtrl C to exit\n\r";
TCHAR cBuffer_in[80];
// Display message on console
printf("\nOpening COM2: Serial Port - Type ctrl C on other device to exit\n\r");
// Open Serial Port COM2: for Read and Write
hSerial = CreateFile(_T("COM2:"), GENERIC_READ | GENERIC_WRITE, 0, NULL,
OPEN_EXISTING, 0, NULL);
// Check for file open errors
if (hSerial == INVALID_HANDLE_VALUE){
printf("file open errors\n");
Sleep(4000);
return 0;
}
// Modify Com Port settings (i.e. Baud Rate, #bits, parity etc)
if(!ModifyCommSettings (hSerial)){
printf("com port settings errors\n");
Sleep(4000);
return 0;
}
// Write to title out to serial port.
if (!WriteFile(hSerial, cBuffer_out, strlen(cBuffer_out), &cBytes_out, NULL)) {
printf("file write errors\n");
Sleep(4000);
return 0;
}
// Set Communication event mask for WaitCommEvent for rxchar (recieve character) in buffer
SetCommMask(hSerial, EV_RXCHAR | EV_ERR);
cBuffer_in[0] = 0;
// Read in characters, copy to console display and Echo
// Loop until ctrl C is typed
while (cBuffer_in[0] != 0x03){
// Wait for character in input buffer - events are more efficient than looping
WaitCommEvent(hSerial, &dwMask, 0);
cBytes_in = 1;
// Loop just in (rare) case more than one character is in UART input buffer
while (cBytes_in != 0){
// Read back data any serial data and display
if (ReadFile(hSerial, cBuffer_in, 79, &cBytes_in, NULL)){
if (cBytes_in == 0) break;
// Display Data read back
printf("%s",cBuffer_in, cBytes_in);
// Echo characters back to sender
if (!WriteFile(hSerial, cBuffer_in, cBytes_in, &cBytes_out, NULL)){
printf("\rfile write errors\n");
Sleep(4000);
return 0;
}
}
}
}
// Close File
CloseHandle(hSerial);
return 1;
}
BOOL ModifyCommSettings (HANDLE hComPort)
{
COMMTIMEOUTS ctos;
DCB PortDCB;
// Initialize the DCBlength member.
PortDCB.DCBlength = sizeof (DCB);
// Get the default serial port settings DCB information.
GetCommState (hSerial, &PortDCB);
// Change the common DCB structure settings to modify serial port settings.
PortDCB.BaudRate = 9600; // Current baud
PortDCB.fBinary = TRUE; // Binary mode; no EOF check
PortDCB.fParity = TRUE; // Enable parity checking
PortDCB.fOutxCtsFlow = FALSE; // No CTS output flow control
PortDCB.fOutxDsrFlow = FALSE; // No DSR output flow control
PortDCB.fDtrControl = DTR_CONTROL_ENABLE; // DTR flow control type
PortDCB.fDsrSensitivity = FALSE; // DSR sensitivity
PortDCB.fTXContinueOnXoff = TRUE; // XOFF continues Tx
PortDCB.fOutX = FALSE; // No XON/XOFF out flow control
PortDCB.fInX = FALSE; // No XON/XOFF in flow control
PortDCB.fErrorChar = FALSE; // Disable error replacement
PortDCB.fNull = FALSE; // Disable null stripping
PortDCB.fRtsControl = RTS_CONTROL_ENABLE; // RTS flow control
PortDCB.fAbortOnError = FALSE; // Do not abort reads/writes on error
PortDCB.ByteSize = 8; // Number of bits/byte, 4-8
PortDCB.Parity = NOPARITY; // 0-4=no,odd,even,mark,space
PortDCB.StopBits = ONESTOPBIT; // 0,1,2 = 1, 1.5, 2
// Configure the port settings according to the new specifications
// of the DCB structure.
if (!SetCommState (hSerial, &PortDCB)){
printf("Unable to configure the serial port");
Sleep(4000);
return false;
}
// Set read time outs
ctos.ReadIntervalTimeout = MAXDWORD;
ctos.ReadTotalTimeoutMultiplier = MAXDWORD;
ctos.ReadTotalTimeoutConstant = 1;
ctos.WriteTotalTimeoutMultiplier = 0;
ctos.WriteTotalTimeoutConstant = 0;
if(!SetCommTimeouts(hSerial, &ctos)){
printf("Unable to configure the serial port");
Sleep(4000);
return false;
}
return true;
}
If you need a GUI, it is easier to develop GUIs using the VS design tools available for C#. Here is a short C# serial port demo
//C# console application serial port demo
using System;
using System.Collections.Generic;
using System.Text;
using System.IO.Ports;
namespace Hello_CS_Serial_World
{
class Program
{
static void Main(string[] args)
{
SerialPort _serialPort;
// Create a new SerialPort object with desired settings.
_serialPort = new SerialPort();
//Defaults to ("COM1", 9600, Parity.None, 8, StopBits.One)
_serialPort.Open();
_serialPort.WriteLine("Hello CS Serial World");
_serialPort.Close();
}
}
}
qiuhong wan.
4
replies
hi all, i'm working in a project where i need to send data acquired from the sensors connected to mbed to a computer, and then read the recieved data through the serial usb communication, and then manipulate these values in some way and send them back to the mbed to take ceratin actions.
my problem is that i can't achieve the communication between the mbed and the computer using a custom made c++ code. can any one help writing the code or tell me how i can deal with serial messages comming through serial port using c++?
thank you very much in advance.
best regards, hassan ali.