Electronic – Does transmitting break over FTDI chipset yield a binary 0 received on the receiving end

Even if it the problem with this particular setup was something else (as pointed out by another answer), another common reason is that the controller is being operated outside the "safe operating area" with respect to Vcc VS clock speed.

With 18.432 MHz clock speed the device would require at least about 4.2V to function properly.

Without some sort of defined protocol, there is no sure way to determinate the end of a string, except for it being terminated by a carriage return ('\r') and/or linefeed ('\n') character.

You want to try something like this:

#define BUF_LEN 100
char buf [BUF_LEN];
unsigned short i;


i = 0;
while (1)
{
    char ch;
    ch = getChar();
    if (ch != '\n')     // ignore lf's
    {
        if (ch != '\r')
        {
                if (i < BUF_LEN-2)
                {
                    buf[i++] = ch;
                    buf[i] = '\0';
                }
        }
        else
        {
            break;      // string now in buf, terminated w/ '\0'
        }
    }   
}

Some strings don't have line feeds ('\n') so I just generally ignore them and treat carriage returns ('\r') as an end of string.

This code allocates a buffer buf which is 100 characters long. If that is not enough, then increase the number in the #define. Of course the buffer could have been allocated on the heap, but a lot of small microcontrollers don't have enough RAM for a useful heap.

I'm using a routine called getChar to get the character, one by one. Change that to whatever you have available.

The routine is very simple, it just gets characters and stores them in a buffer until a carriage return is found. Then it breaks out of the loop with the string in the buffer, terminated by a 0 ('\0') without any '\r' or '\n' in it.