GE Multilin C70 Capacitor Bank Protection and Control System 3-333 HARDWARE 3.3 DIRECT INPUT/OUTPUT COMMUNICATIONS3d) 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.3.3.5 IEEE C37.94 INTERFACEThe UR-series IEEE C37.94 communication modules (modules types 2I, 2J, 76, and 77) are designed to interface withIEEE C37.94 compliant digital multiplexers or an IEEE C37.94 compliant interface converter for use with direct input andoutput applications. The IEEE C37.94 standard defines a point-to-point optical link for synchronous data between a multi-plexer and a teleprotection device. This data is typically 64 kbps, but the standard provides for speeds up to 64n kbps,where n = 1, 2,…, 12. The UR-series C37.94 communication modules are either 64 kbps (with n fixed at 1) for 128 kbps(with n fixed at 2). The frame is a valid International Telecommunications Union (ITU-T) recommended G.704 pattern fromthe standpoint of framing and data rate. The frame is 256 bits and is repeated at a frame rate of 8000 Hz, with a resultant bitrate of 2048 kbps.The specifications for the module are as follows:.• IEEE standard: C37.94 for 2 × 64 kbps optical fiber interface (for 76 and 77 modules)• Fiber optic cable type: 50 nm or 62.5 μm core diameter optical fiber• Fiber optic mode: multimode• Fiber optic cable length: up to 2 km• Fiber optic connector: type ST• Wavelength: 820 ±40 nm• Connection: as per all fiber optic connections, a Tx to Rx connection is requiredThe UR-series C37.94 communication module can be connected directly to any compliant digital multiplexer that supportsthe IEEE C37.94 standard shown as follows.The UR-series C37.94 communication module can be connected to the electrical interface (G.703, RS422, or X.21) of anon-compliant digital multiplexer via an optical-to-electrical interface converter that supports the IEEE C37.94 standard,shown as follows.In 2008, GE Grid Solutions released revised modules 76 and 77 for C37.94 communication to enable multi-ended faultlocation functionality with firmware 5.60 release and higher. All modules 76 and 77 shipped the change support this featureand are fully backward compatible with firmware releases below 5.60. For customers using firmware release 5.60 andhigher, the module can be identified with "Rev D" printed on the module and is to be used on all ends of C70 communica-tion for two and three terminal applications. Failure to use it at all ends results in intermittent communication alarms. Forcustomers using firmware revisions below 5.60, it is not required to match the revision of the modules installed.UR-seriesdeviceIEEE C37.94fiber interfaceup to 2 km842755A2.CDRDigitalmultiplexer,IEEE C37.94compliantUR-seriesdeviceup to 2 kmIEEE C37.94converterRS422interface842756A2.CDRIEEE C37.94fiber interface Digitalmultiplexerwith EIA-422interface
