Jackie Chan, 8-28-00, briefly describes a proposed modem network consisting of a master and several slaves, each with a unique ID. He asks if modem handshaking is possible and if data can be sent without handshaking.
 
For this application, why is a modem network desired? How is it to be constructed? What are the wire lengths? The connection of many 600 ohm POTS transformers in parallel will need some thought. If the 600 ohm transformer is not used, what is the network interface? The 89C55 serial port has the 9th bit addressing mode that is designed for this type of application. Its operation is clean and simple, especially when compared with the modem. This serial port can be easily connected into a RS-422 network with many slaves over a considerable distance.
 
The Zilog Z02201/Z02922 has DTMF tone detection, which could be used for the slave address selection. Once this connection is established, then the normal handshaking procedures can follow. However, the effort here will be huge when compared with the above 89C55/RS-422 system. The Z02201/2922 programming is not trivial.