For comments & questions..

The main processor have 3 buffers (30 Registers / Character each) 1. Local Buffer. For saving the message before sending.
2. Tx Buffer. For saving the message of Local buffer for Tx.
3. Rx Buffer. For saving and displaying the Rx message.

The Chating terminal have 2 Windows , Upper Window , line 1 & 2 Displays  the Rx message from other user and line  3 & 4 is the Tx message from 1st user.

When first user is typing the message , it appears in lower window and saving in Local Buffer and after pressing the " ENTER < " on keyboard the message is shifting in upper window line 3 & 4 & shifting in Tx Buffer of Main Processor , and clearing the lower window & local buffer , means message is queued for shifting in MODEM.

SCREEN SHOTS

When MODEM is exchanging the buffers then it will shift outgoing message in Tx Buffer and further will be transmitted.

After Transmission of Tx message & Termination Bytes ,The MODEM is waiting for Rx message.

By making two similar units , Now it is possible to exchange the messages .. so you can chat with other user ..

In case , if the Ping / Connectivity is lost , I programmed a key WWW on key board for refreshing the connection. By pressing this key , modem is searching and handshaking with other modem , and once again the ping is started between 2 units.

When 2 units are connected and transmitting / receiving the data , the RED LED is representing the Tx mode , and alternately around in 1 second Tx/Rx is being done.

RF Module    ( BIM-433 / FM-RXQ1-433 ) Baught from Radiometrix or RFSolutions