Serial Communication

Interfacing to any Matrix Orbital Intelligent Serial LCD, Serial VFD, Serial TFT or Serial OLED begins with the correct selection of the serial port and associated attributes. In C++ a serial port object can be defined as a file using the port name, read and write designations, as well as a host of other settings.

port = CreateFile("COM9", GENERIC_READ | GENERIC_WRITE,

0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

Once defined, serial protocol specific attributes can be defined. Most Matrix Orbital Intelligent Serial and USB Displays will run at a default speed of 19200 baud, with 8 bits of data, no parity bit, and 1 stop bit. Again, especially with older Intelligent Serial Displays, flow control should be turned off, but please consult your display manual to confirm.

GetCommState(port, &port_attributes);

port_attributes.BaudRate = CBR_19200;

port_attributes.ByteSize = 8;

port_attributes.Parity = NOPARITY;

port_attributes.StopBits = ONESTOPBIT;

port_attributes.fRtsControl = RTS_CONTROL_DISABLE;

SetCommState(port, &port_attributes);

Finally, if information is to be read from the serial port it is important to set the timeout value. This will ensure that the program will not wait infinitely for a byte to be read should an error occur.

timeouts.ReadIntervalTimeout = 500;

SetCommTimeouts(port, &timeouts);

Once a port is selected and its attributes set, text can easily be transmitted to an attached Intelligent Serial Display.

Text

Once a serial port file is created and configured, text can be written to it as a series of bytes. In C++ a byte is defined as a char, adding the unsigned stipulation allows the extended table to be used.

unsigned char message[] = "Hello World!";

WriteFile(my_port, &message, sizeof(message), &bytes_written, NULL);

Once defined, an array can be written to the Intelligent Serial Display by specifying the port, referencing the array, indicating the number of bytes to send, and providing a place to record the number of bytes written.

Commands

Commands are transmitted in very much the same way as text. However, as they are often unprintable characters, they are usually defined within an array of bytes as decimal or hexadecimal values.

unsigned char command[] = {254, 88};

WriteFile(port, &command, sizeof(command), &bytes, NULL);

Again, the values are written to the serial port in the same way as a series of text characters.

On Reading

The easiest way to read key presses from a Matrix Orbital Intelligent Serial Display is to use polling mode. First, turn off the auto transmission of key presses so they stay in the ten key buffer rather than being transmitted immediately to the serial port.

unsigned char command[] = {254, 79};

WriteFile(port, &command, sizeof(command), &bytes, NULL);

Next, ensuring a key has been pressed, issue the command to poll the Intelligent Serial Display. This will result in the key press being transmitted to the host.

unsigned char command[] = {254, 38};

if(WriteFile(port, &command, sizeof(command), &bytes, NULL))

Finally, read a single byte from the serial port file. If there are additional keys in the buffer, the most significant bit of the value will be a one, if there are no further keys in the buffer it will be zero.

return(ReadFile(port, key, sizeof(key), &bytes, NULL));

else

       return(false);

In Closing

Once all transactions with an attached Intelligent Serial Display are complete using the serial port file, it should be closed before exiting the program.

CloseHandle(port);

With this all input and output aspects of a Matrix Orbital Intelligent Serial display have been explored in the C++ programming environment. These concepts provide a scratchpad from which an epic tome of HMI applications may be adapted for your Matrix Orbital Intelligent Serial or USB Display.