Hi Sandeep,
Sorry for the delayed response.
I found this from your ISR;
if(ch!=0x0D && ch!= 0x0A)
{
str[count++]=ch;
lcd_data(str[count-1]);
}
ISR should always be very light, less time consuming and free of any function calls. Hence I suggest you to avoid the statement;
lcd_data(str[count-1]);
from your ISR and try.
The function will still be executing even if the next interrupt happens and I guess that could be the reason.