3-34 L30 Line Current Differential System GE Multilin3.3 PILOT CHANNEL COMMUNICATIONS 3 HARDWARE3d) RECEIVE TIMINGThe RS422 interface utilizes NRZI-MARK modulation code and; therefore, does not rely on an Rx clock to recapture data.NRZI-MARK is an edge-type, invertible, self-clocking code.To recover the Rx clock from the data-stream, an integrated DPLL (digital phase lock loop) circuit is utilized. The DPLL isdriven by an internal clock, which is 16-times over-sampled, and uses this clock along with the data-stream to generate adata clock that can be used as the SCC (serial communication controller) receive clock.3.3.6 RS422 AND FIBER INTERFACEThe following figure shows the combined RS422 plus Fiber interface configuration at 64K baud. The 7L, 7M, 7N, 7P, and 74modules are used in two-terminal with a redundant channel or three-terminal configurations where channel 1 is employedvia the RS422 interface (possibly with a multiplexer) and channel 2 via direct fiber.AWG 24 twisted shielded pair is recommended for external RS422 connections and the shield should be grounded only atone end. For the direct fiber channel, power budget issues should be addressed properly.When using a LASER Interface, attenuators may be necessary to ensure that you do not exceed maximumoptical input power to the receiver.Figure 3–39: RS422 AND FIBER INTERFACE CONNECTIONConnections shown above are for multiplexers configured as DCE (data communications equipment) units.3.3.7 G.703 AND FIBER INTERFACEThe figure below shows the combined G.703 plus fiber interface configuration at 64 kbps. The 7E, 7F, 7G, 7Q, and 75 mod-ules are used in configurations where channel 1 is employed via the G.703 interface (possibly with a multiplexer) and chan-nel 2 via direct fiber. AWG 24 twisted shielded pair is recommended for external G.703 connections connecting the shield topin 1a at one end only. For the direct fiber channel, power budget issues should be addressed properly. See previous sec-tions for additional details on the G.703 and fiber interfaces.When using a laser Interface, attenuators may be necessary to ensure that you do not exceed the maxi-mum optical input power to the receiver.Figure 3–40: G.703 AND FIBER INTERFACE CONNECTIONWARNING~~~~~~~~~ShieldCOMTx1 +Tx1 –Rx1 –Rx1 +1a2b3a4bFiberchannel 2Clock(channel 1)RS422channel 1Surge1b2a3b6a8aTx2 Rx2Inter-relay comms. 7L, 7M, 7N, 7P, 74842777A1.CDRWARNING~~~~~~ShieldTx –Tx +Rx –Rx +1a2a3aFiberchannel 2G.703channel 1Surge1b2b3bTx2Rx2Inter-relaycommunications 7E, 7F, 7G,7Q,75842778A1.CDR
