Hard to say without knowing more about your LED matrix. If it's something you've built then you can print anything you'd like on it.
Its a matrix based on the Holtek HT1632. The Arduino controls it. Forgot to mention!
It what way?
It prints garbage characters, as you said.
The AVR compilier supports eight-bit characters. Traditionally, the first 127 characters are ASCII. Using your example as an example, it's up to the reciever to decide how those eight-bits are interpreted.
What I want to do is make the Arduino print Greek characters on the matrix. I have a function that reads the "font" from an array and then print the corresponding character on the display. I want to extend this function and make it print more characters. The array contains the printable ASCII characters.
This is what came into my mind after your reply. I'll make another array containing the Unicode characters and modify the function to use that array when needed. Will that work, considering that Unicode chars use 16bits?
EDIT:
The serial port of the Arduino can only sent bytes (value 0..255) over the line. The receiving application interpret these byte values - typically as ASCII, however you are free to use another interpretation including Greek characters. The Arduino does not know, it just send bytes.
It's similar to writing a word document, selecting all and change the font to Greek. The (underlying) bytes won't change, but the interpretation and visualization is changed.
Several LCD screens have the option to define your own characterset. If there are enough free definable chars in the LCD you could define the whole greek alphabet.
If you are sending the data to a PC/Mac, it is up to the receveing app to translate the byte to greek.Hopes this helps.
Thanks! Yes it helped me clear some things 