SEND_RS232("+++ATE0\r",10);
Код
Escape sequence Char value Description
\a 7 Attention (bell)
\b 8 Backspace
\t 9 Horizontal tab
\n 10 New line (line feed)
\v 11 Vertical tab
\f 12 Form feed
\r 13 Carriage return
\xnn 0xnn ASCII code in hexadecimal
\nnn 0nnn ASCII code in octal
Это написано в любом букваре по 'C'.