Serial communication c++ - c++

Question

I'm trying do some serial communication between my pc and an arduino ATmega2560
First the microntroller's program :
void setup() {
Serial.begin(9600);
}
void loop() {
Serial.write('A');
}
The arduino program is very basic, his aim is to check the next program which is on the pc.
The main.cpp :
#include <iostream>
#include "SerialPort.h"
using namespace std;
int main()
{
SerialPort port("com3", 9600);
while (1)
{
//Receive
unsigned char dataR;
port.receive(dataR, 1);
cout << dataR << endl;
}
return 0;
}
The SerialPort.h:
#include <windows.h>
#include <iostream>
class SerialPort
{
public:
//Constructors
SerialPort();
SerialPort(const char* port, unsigned long BaudRate);
//Initialization
void Initialize(const char* port, unsigned long BaudRate);
//Serial I/O
void receive(unsigned char &data, unsigned int byteSize);
void transmit(unsigned char *data, unsigned int byteSize);
//State
void connect();
void disconnect();
bool isConnected();
//Destructor
~SerialPort();
private:
HANDLE handler;
bool isConnect;
};
And the SerialPort.cpp :
#include "SerialPort.h"
/*Constructors*/
SerialPort::SerialPort()
: isConnect(false) {}
SerialPort::SerialPort(const char* port, unsigned long BaudRate)
: isConnect(false)
{
Initialize(port, BaudRate);
}
/*Initialization*/
void SerialPort::Initialize(const char* port, unsigned long BaudRate)
{
handler = CreateFile(port, GENERIC_READ | GENERIC_WRITE, NULL, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if (handler == INVALID_HANDLE_VALUE)
{
std::cout << "ERROR!::Error during opening port" << port << std::endl;
return;
}
DCB serialParameters;
if (!GetCommState(handler, &serialParameters)) /*Get com parameters*/
{
std::cout << "ERROR!::failed to get current serial parameters" << std::endl;
return;
}
serialParameters.DCBlength = sizeof(DCB);
serialParameters.BaudRate = BaudRate;
serialParameters.ByteSize = 1; /*8 bit data format*/
serialParameters.StopBits = TWOSTOPBITS;
serialParameters.Parity = PARITY_NONE;
if (!SetCommState(handler, &serialParameters)) /*Send modified com parameters*/
{
std::cout << "ALERT!:Failed to set THE Serial port parameters" << std::endl;
return;
}
isConnect = true;
PurgeComm(handler, PURGE_RXCLEAR | PURGE_TXCLEAR);
}
/*Serial I/O*/
void SerialPort::receive(unsigned char &data, unsigned int byteSize)
{
ReadFile(handler, &data, byteSize, NULL, NULL);
}
void SerialPort::transmit(unsigned char *data, unsigned int byteSize)
{
WriteFile(handler, data, byteSize, NULL, NULL);
}
/*State*/
void SerialPort::connect()
{
isConnect = true;
}
void SerialPort::disconnect()
{
isConnect = false;
}
bool SerialPort::isConnected()
{
return isConnect;
}
/*Destructors*/
SerialPort::~SerialPort()
{
if (isConnect)
{
isConnect = false;
CloseHandle(handler);
}
}
I've an issue with this program : I don't receive the right data. Where I should get on the terminal
A
A
A
...
I get weird characters made of ? in a square
I hope you understood my problem
Thanks

Answer 1

The DCB ByteSize parameter is in bits. You have specified a UART frame with one data bit - which is not supported by the hardware at either end.
For a conventional N,8,1 data frame, use
serialParameters.ByteSize = 8 ;
serialParameters.StopBits = ONESTOPBIT ;
serialParameters.Parity = NOPARITY ;
ByteSize is perhaps a misleading name. It defines the number of bits between the start and stop bit in an UART frame. Most commonly this is 8, but for pure ASCII data transfer 7 might be used - historically at least.
The Atmel AVR UART supports frames with 5 to 9 data bits. The PC's UART may be virtual, but will typically be compatible with the 16550 UART, which supported 5 to 8 bit data frames, however these days you are more likely to be using USB-Serial adapter, and the UART on the USB/Serial bridge may not support all 16550 modes - the common FTDI232R for example only supports 7 or 8 bit frames, while Prolific PL2303 supportts 5 to 8. It probably pays to avoid unconventional frames and stick to N,8,1 if you want to be sure it will work on a range of hardware.

Answer 2

From the Arduino documentation on Serial.begin() (emphasis added):
An optional second argument configures the data, parity, and stop
bits. The default is 8 data bits, no parity, one stop bit.
I see this in your code (with no second parameter):
Serial.begin(9600);
and this
serialParameters.StopBits = TWOSTOPBITS;
I think that may be your problem.