It must be one of the following characters (not case-sensitive):
 
   N - no Debug files are produced 
   C - the .MCC file is produced.  This file is translated 
       source suitable for separate compilation. 
   D - the .MCD file is produced.  This file is useful in 
       debugging preprocessor behavior. 
   B - both the .MCC and .MCD files are produced. 
   0 - not specified