ok so I understood something. When the characters I send are larger than 127 (so when the 8th bit is a 1: ex. 10000000 and larger), Matlab doesn't send the right number. This is why everything worked well for most of the characters, but as soon as I send a value larger than 127 (80 in hex) it didn't work properly.
Does someone know how I can avoid this? I guess Matlab considers the 8th bit as a sign or something...
Thank you!