Yep, that seems to work. Thanks Erik.

It appears that the solution is to place all module-wide configurations in a separate header file, and then to #include this file in the parent module, as well as in each of the, possibly numerous, sub-component header files.

//file Sio_poll_config.h

#ifndef SIO_POLL_CONFIG_H
#define SIO_POLL_CONFIG_H

#define SIO_POLL_CONFIG_XTAL             22118400

#endif

//file Sio_poll.h

#ifndef SIO_POLL_H
#define SIO_POLL_H

#include "Delay.h"
#include "Sio_poll_config.h"

#define SIO_POLL_XTAL             SIO_POLL_CONFIG_XTAL

#endif

//file Delay.h

#ifndef DELAY_H
#define DELAY_H

#include "Sio_poll_config.h"

#define DELAY_XTAL         SIO_POLL_CONFIG_XTAL

#endif

Configuring only a single, module-wide header file makes a lot more sense than repeatedly adjusting both parent and, possibly numerous, component module headers. I'm happy. :-)

Regards,
Murray R. Van Luyn.