Method and apparatus for testing in FDM system

Details Method and apparatus for testing in FDM system Method and apparatus for testing in FDM system

1975-03-03

1976-04-20

Olms, Douglas W.

179 2DP, 1791753R, H04M 1100

Patent

active

039521630

ABSTRACT:
A data communication system is described in which dial access control signals such as RING, DATA SET READY, DATA TERMINAL READY, CARRIER DETECT, and OUT OF SERVICE are transmitted between a central processing unit (CPU) and remote terminals in the form of frequency-modulated signals. A special frequency signal is transmitted from a remote terminal whenever a RING or DATA SET READY control signal is present and a CARRIER DETECT signal is not. Preferably, this special frequency is midway between the center frequency used for data communication and the frequency of either the MARK or the SPACE signal. Upon reception, this special frequency signal is processed in a particular fashion to generate signals comparable to the RING or DATA SET READY signals of the prior art. DATA TERMINAL READY and CARRIER DETECT control signals are transmitted as carrier signals and the OUT OF SERVICE signal is transmitted as a center frequency signal. Suitable processing at the receiver forms these signals into signals comparable to those of the prior art. Advantageously, the OUT OF SERVICE signal is used with appropriate apparatus to initiate testing of the remote terminal. Circuitry in this apparatus permits one to switch repeatedly from testing of just an FDM transmitter/receiver in the remote terminal to testing of both the FDM transmitter/receiver and a modem.

REFERENCES:
patent: 3655915 (1972-04-01), Liberman et al.
patent: 3692939 (1972-09-01), Knight et al.
patent: 3743938 (1973-07-01), Davis
patent: 3769454 (1973-10-01), Liberman et al.

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