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(I) Programming serial port communications

This entry is part 1 of 2 in the series Serial communications

250px-Serial_portConnections and operating system symbolic names

A serial port is a communication physical interface through which information  transfers in or out one bit at a time (in contrast to a parallel port) being, more or less compliant, with the RS-232 standard.

But serial port communications aren’t only useful for wired DE-9 connectors. it also allows us to use it with USB (ftdi), Bluetooth (serial profile) and Zigbee using virtual serial ports.

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Types-usbSerial and virtual serial ports appear as  COMx in Windows operating systems (COM1, COM2, …) andin UNIX/Linux as ttySx or ttyUSBx or even ttyACMx (ttyS0, ttyS1, ttyUSB0, ttyUSB1, ttyACM0, ttyACM1,…).

For programming purposes we usually want to communicate computers with others computers, microcontrollers or other devices like GPS, LED or LCD displays.

·

Serial port programming in C/C++, Windows and Linux

Using the serial port is a lot  easier, but sometimes tricky. The basic commands are to open a connection, read and write over this connection and, finally, tom close it, better if using the C++ RAII idiom.

winWindows commands:
Here you can find a complete C++ for Windows example.

With these next two definitions (among others needed):

HANDLE
serialPortHandle
wchar_t* device

serialPortHandle = CreateFile(device, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, NULL, NULL);
if (serialPortHandle!=INVALID_HANDLE_VALUE)
ReadFile(serialPortHandle, buffer, len, &read_nbr, NULL);

if (serialPortHandle!=INVALID_HANDLE_VALUE)
WriteFile(serialPortHandle, buffer, len, &result, NULL);
CloseHandle(serialPortHandle);

linuxUnix/Linux commands:
Here you can find a complete C++ for Linux example.

With these two definitions:

·
int fileDescriptor;
char *device;
·
·
  • Opening a connection, open
struct termios terminalAttributes;

fileDescriptor = open(device, O_RDWR | O_NOCTTY | O_NDELAY | O_FSYNC );

// clear terminalAttributes data
memset(&terminalAttributes, 0, sizeof(struct termios));

terminalAttributes.c_cflag = B57600 | CS8 | CLOCAL | CREAD; 
terminalAttributes.c_iflag = IGNPAR |  ONLCR;
terminalAttributes.c_oflag = OPOST;
terminalAttributes.c_cc[VTIME] = 0;
terminalAttributes.c_cc[VMIN] = 1;

tcsetattr(fileDescriptor, TCSANOW, &terminalAttributes);
int n=read(fileDescriptor, buffer, len);

int n=write(fileDescriptor, buffer, len);
  • Closing the connection, close
close(fileDescriptor);

More information:

https://en.wikipedia.org/wiki/Serial_communication
http://en.wikipedia.org/wiki/Serial_port

http://www.lvr.com/serport.htm
http://digilander.libero.it/robang/rubrica/serial.htm
http://en.wikibooks.org/wiki/Serial_Programming

http://msdn.microsoft.com/en-us/library/ff802693.aspx

Simple C++ class example using serial port, USB, wireless…

This entry is part 2 of 2 in the series Serial communications

This post is part of the Practical C++ programming tutorial for Bioloid

Here you can find a post serie about using serial port communications with C/C++ and C#, for Windows, Linux and microcontrollers.
This code is for Windows and Visual Studio and can be used for serial cable communications, USB2Dynamixel and indeed Zigbee:

Header:

class SerialPort {
private:
HANDLE serialPortHandle;

public:
SerialPort();
~SerialPort();

int connect ();
int connect (wchar_t *device);
//int connect (char *deviceName, int baudRate, SerialParity parity);
void disconnect(void);

int sendArray(unsigned char *buffer, int len);
int getArray (unsigned char *buffer, int len);

void clear();
};

Body:


SerialPort::SerialPort() {
serialPortHandle = INVALID_HANDLE_VALUE;
}

SerialPort::~SerialPort() {
if (serialPortHandle!=INVALID_HANDLE_VALUE)
CloseHandle(serialPortHandle);

serialPortHandle = INVALID_HANDLE_VALUE;
}

int SerialPort::connect() {
return connect(L"COM1");
}

int SerialPort::connect( wchar_t* device) {
int error=0;
DCB dcb;

memset(&dcb,0,sizeof(dcb));

dcb.DCBlength = sizeof(dcb);

dcb.BaudRate = 57600;
dcb.Parity = NOPARITY;
dcb.fParity = 0;
dcb.StopBits = ONESTOPBIT;
dcb.ByteSize = 8;

serialPortHandle = CreateFile(device, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, NULL, NULL);

if (serialPortHandle != INVALID_HANDLE_VALUE) {
if(!SetCommState(serialPortHandle,&dcb))
error=2;
}
else {
error=1;
}

if (error!=0) {
disconnect();
}
else {
clear();
}

return error;
}

void SerialPort::disconnect(void) {
CloseHandle(serialPortHandle);
serialPortHandle = INVALID_HANDLE_VALUE;

//printf("Port 1 has been CLOSED and %d is the file descriptionn", fileDescriptor);
}

int SerialPort::sendArray(unsigned char *buffer, int len) {
unsigned long result;

if (serialPortHandle!=INVALID_HANDLE_VALUE)
WriteFile(serialPortHandle, buffer, len, &result, NULL);

return result;
}

int SerialPort::getArray (unsigned char *buffer, int len) {
unsigned long read_nbr;

read_nbr = 0;
if (serialPortHandle!=INVALID_HANDLE_VALUE)
{
ReadFile(serialPortHandle, buffer, len, &read_nbr, NULL);
}

return((int) read_nbr);
}

void SerialPort::clear() {
PurgeComm (serialPortHandle, PURGE_RXCLEAR | PURGE_TXCLEAR);
}
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