// COM port test, for all types of MT chips
// Action: Echo received characters back to PC.
// If there is only one COM port available on the MT chip, no need to specify the COM port number.
// By default, the MT system selects the first available COM port.

main()
{
    int    d;

//    sys(0, 0);                                  // select COM port 0
//    sys(0, 1);                                  // select COM port 1
//    sys(0, 2);                                  // select ARM 1st virtual USB-COM port
//    sys(0, 3);                                  // select ARM 2nd virtual USB-COM port

    writes("9600", 500);
    setcomm(9600);                		// enable COM and set baudrate at 9600,8N1
    loop {
        do d = readm(232, 0); while(d == -1);   // wait to receive a character
        writec(0, d, 10);        		// display it, comment this out to run faster!
        writec(232, d, 0);      		// echo it back to sender
        if(d == '?') writes("$Hi!", 100);       // output a message to COM if '?' is received
        if(d == '!') break;       		// exit if '!' received
    }
    writes("$end", 200);
    setcomm(0);                   		// disable Comm
    writes("end", 2000);
}