第5套 Data communications equipment(DEC) (1) the serial data stream from the DTE and converts it to some form of (2) suitable of transmission on voice grade lines. At the (3),the DCE performs the reverse function of convering the received analog signal to serial digital data stream .The simplest form of DCE is a (4) or data set . At the transmit end, the modem can be considered a form of (5),while at the receive end, it can be considered a form of analog to digital converter. The most common forms of modulation by modems are frequency shift keying(FSK),phase shift keying(PSK) ,and quadrature amplitude modulation(QAM). If the cables and signal levels used to interconnect the DTE and DCE were left unregulated,the variations generated would probably be proporation to the number of manufactures. Electronics Industries Association(EIA) ,an organization of manufactuuers concerned with establishing industry standards,have agreed on the RS-232C as the standard interface between the DTE and the modem .This is a 25 pin cable pins have designated funtons and specified signal levels. (1) A. accepts B.sends C.delivers D.receives (2) A. digital signal B.analog signal C.light signal D.sound signal (3) A. back end B.front end C.sending end D.receive end (4) A. modem B.cpu C.demodulator D.modulator. (5) A. host computer B.digital to analog converter C. analog to digital converter D.secondaries 答案: 1:A,2:B,3:D,4:A,5:B
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