Part 2

Interface Concepts 639Interchange Circuit FunctionsThere are four categories of interchange circuits: Ground, Timing, Data, and Control.With the exception of the grounds, they can originate either in the modem (DataCommunications Equipment, or DCE) or in the computer (Data Terminal Equipment,or DTE).Ground CircuitsCircuit AA (CCITT 101)Protective Ground: Electrically connected to the frame of theequipment and to earth ground as external regulationsdemand.Circuit AB (CCITT 102)Signal Ground: The zero-voltage reference point. Also actsas the common return for unbalanced interchange circuits.Timing CircuitsThe clock generated by the Data Terminal Equipment:Circuit DA (CCITT 1 13)Transmitter Signal Element Timing: Provides timing for thetransmitted data on Circuit BA (CCITT 103). A transition fromON to OFF (positive to negative) indicates the approximatecenter of each signal element.The clocks generated by Data Communications Equipment:Circuit DB (CCITT 1 14)Transmitter Signal Element Timing: Provides DTE with a timingsignal to be used with the transmitted data on Circuit BA(CCITT 103). A transition from OFF to ON (negative topositive) indicates the transition between signal elements.Circuit DD (CCITT 1 15)Receiver Signal Element Timing: Provides timing for thereceived data on Circuit BB (CCITT 104). The transition fromON to OFF (positive to negative) indicates the approximatecenter of each signal element.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com