GE Multilin L90 Line Differential Relay 3-253 HARDWARE 3.3 L90 CHANNEL COMMUNICATION3e) TEST MODES (SWITCHES S5 AND S6)MINIMUM REMOTE LOOPBACK MODE:In Minimum Remote Loopback mode, the multiplexer is enabled to return the data from the external interface without anyprocessing to assist in diagnosing G.703 Line Side problems irrespective of clock rate. Data enters from the G.703 inputs,passes through the data stabilization latch which also restores the proper signal polarity, passes through the multiplexerand then returns to the transmitter. The Differential Received Data is processed and passed to the G.703 Transmitter mod-ule after which point the data is discarded. The G.703 Receiver module is fully functional and continues to process data andpasses it to the Differential Manchester Transmitter module. Since timing is returned as it is received, the timing source isexpected to be from the G.703 line side of the interface.DUAL LOOPBACK MODE:In Dual Loopback Mode, the multiplexers are active and the functions of the circuit are divided into two with each Receiver/Transmitter pair linked together to deconstruct and then reconstruct their respective signals. Differential Manchester dataenters the Differential Manchester Receiver module and then is returned to the Differential Manchester Transmitter module.Likewise, G.703 data enters the G.703 Receiver module and is passed through to the G.703 Transmitter module to bereturned as G.703 data. Because of the complete split in the communications path and because, in each case, the clocksare extracted and reconstructed with the outgoing data, in this mode there must be two independent sources of timing. Onesource lies on the G.703 line side of the interface while the other lies on the Differential Manchester side of the interface.3.3.5 RS422 INTERFACEa) DESCRIPTIONThe following figure shows the RS422 2-terminal interface configuration at 64 kbps. AWG 22 twisted shielded pair is recom-mended for external connections. This interface module is protected by surge suppression devices which optically isolated.The RS422 module is fixed at 64 kbps only. The SETTINGS ! PRODUCT SETUP !" DIRECT I/O !" DIRECT I/O DATARATE setting is not applicable to this module.SHIELD TERMINATIONThe shield pins (6a and 7b) are internally connected to the ground pin (8a). Proper shield termination is as follows:Site 1: Terminate shield to pins 6a and/or 7b; Site 2: Terminate shield to ëCOMí pin 2b.DMRDMXG7XG7RDMR = Differential Manchester ReceiverDMX = Differential Manchester TransmitterG7X = G.703 TransmitterG7R = G.703 ReceiverDMRDMXG7XG7RDMR = Differential Manchester ReceiverDMX = Differential Manchester TransmitterG7X = G.703 TransmitterG7R = G.703 ReceiverNOTE
