As I remember, <ctrl-Z> has decimal ASCII code 26.
so it should look like:

code unsigned char AT6[] = "FIRE ALERT x1A*";

BTW, why do you use asterisk as a marker of the end of string? In C-language the string constant between "" has the 0x00 at the end. So your loops may avoid to check for '*' but just look at zero, something like this:

while (*ptr0)
{ 
SBUF = *ptr0++; 
while(!TI) 
{} 
TI = 0;
}

Regards,
Oleg