indexer lpt question?

I would like to find out if it is possable to interface the indexer lpt
software with a commercial CNC machine. The commercial CNC is a
Milltronics machine with a CEN5 control (dos based machine) it has a
rs232 port that is never used. What I would be interested in doing is
have the CNC do some xyz moves. When the cnc saw an M code it would
then send a code to the indexer where it would then index so many
degrees and then the indexer would send back a index complete signal
back to the cnc so that it would then continue to prosess the rest of
the code in the CNC machine until it saw another m code where the
indexer would again take control and so on.

Thanks
Stan