Here so-called tail circuit cable is needed, but this is a very uncommon kind of connection. The third kind of connections is DCE-DCE. For that kind of connection, so-called null-modem connection is needed actually this connection is done in this project. The other kind of common connection is a DTE-DTE connection, for instance connection between two PCs, in order to exchange data between them. In null modem mode, a minimal 3-wire RS-232 port consisting only of transmit data, receive data and ground is commonly used when the full facilities of RS-232 are not required. The null-modem configuration simplifies the handshaking between computers. Null modem is a communication method to connect two DTEs (computer, terminal, printer, etc) directly using RS-232 serial cable.

The original RS-232 standard defined only the connection of DTEs with DCEs, i.e., modems. RS-232 is a standard for serial binary data transfer between a data terminal equipment (DTE) and a data circuit-terminating equipment (DCE), commonly used in computer serial ports. Serial communication is the process of sending data sequentially one bit at a time, over a communication channel or computer bus.

Borland c 4.5