Robin2:
The Serial Monitor is just eavesdropping on the conversation between the Arduino and the XBee.You can connect several listeners to a single Serial TX line. However adding several "talkers" to a single RX line requires some additional components.
...R
Oh that makes it clear ... eavesdropping !! Never realized that this was possible ( one to many and many to one )on a serial link. Thanks !
If that be the case then who do some terminals complain that the "Port is already open " when you try to connect to such a link up between two items ?