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3 HARDWARE
To recover the Rx clock from the data-stream, an integrated DPLL (digital phase lock loop) circuit is utilized. The DPLL is
driven by an internal clock, which is 16-times over-sampled, and uses this clock along with the data-stream to generate a
data clock that can be used as the SCC (serial communication controller) receive clock.
The UR-series IEEE C37.94 communication modules (modules types 2G, 2H, 76, and 77) are designed to interface with
IEEE C37.94 compliant digital multiplexers or an IEEE C37.94 compliant interface converter for use with direct input and
output applications for firmware revisions 3.30 and higher. The IEEE C37.94 standard defines a point-to-point optical link
for synchronous data between a multiplexer 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 from the standpoint of framing and data rate. The frame is 256 bits and is repeated at
a frame rate of 8000 Hz, with a resultant bit rate of 2048 kbps.
The specifications for the module are as follows:.
IEEE standard: C37.94 for 1 × 128 kbps optical fiber interface (for 2G and 2H modules) or C37.94 for 2 × 64 kbps opti-
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cal fiber interface (for 76 and 77 modules).
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Fiber optic cable type: 50 mm or 62.5 mm core diameter optical fiber.
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Fiber optic mode: multi-mode.
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Fiber optic cable length: up to 2 km.
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Fiber optic connector: type ST.
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Wavelength: 830 ±40 nm.
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Connection: as per all fiber optic connections, a Tx to Rx connection is required.
The UR-series C37.94 communication module can be connected directly to any compliant digital multiplexer that supports
the IEEE C37.94 standard as shown below.
The UR-series C37.94 communication module can be connected to the electrical interface (G.703, RS422, or X.21) of a
non-compliant digital multiplexer via an optical-to-electrical interface converter that supports the IEEE C37.94 standard, as
shown below.
GE Multilin
C70 Capacitor Bank Protection and Control System
3.3 DIRECT INPUT/OUTPUT COMMUNICATIONS
3.3.5 IEEE C37.94 INTERFACE
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