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]
Com base no texto, necessita(m) ser verificado(s), antes
de uma transmissão de informação para o modem, o(s)
seguinte(s) sinal(is):