Considerando o seguinte trecho do texto: “most of the modem control...

The Modem Handshake

 Modem control software has to test the condition of the CTS and DSR signals before transmitting information to the modem. The modem also has to be conditioned by the computer by applying a logic zero on the modem connections DTR and RTS .
If one of the two communications interface adapters discussed earlier in this chapter is used, most of the modem control is already accomplished by these devices. For example, the Intel 8251A has all four of the pin connections required for modem control, while the Motorola MC6850 contains only some of the connections.

[Extraído de: Microprocessors and Peripherals, Barry B. Brey, Maxwell Macmillan International Editions, 1991]