GE D90 Plus Instruction Manual page 75

CHAPTER 3: INSTALLATION
Fiber communications interface
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 36: Clock and data transitions
The 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 is driven by an internal clock, which is 16-times oversampled,
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.
Plus
The UR -series communication module is 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 when the
direct fiber interfaces using the Differential Manchester protocol when the
setting is "Direct Fiber". The IEEE C37.94 standard defines a point-to-point optical
Encoding
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.
Plus
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 2 × 64/128 kbps optical fiber interface.
• Differential Manchester protocol: 2 × 64/128 kbps optical fiber interface.
• Fiber optic cable type: 50 mm or 62.5 mm core diameter optical fiber.
• Fiber optic mode: multi-mode.
• Fiber optic cable length: up to 2 km.
• Fiber optic connector: type ST.
• Wavelength: 850 nm VCSEL laser.
• Connection: as per all fiber optic connections, a Tx to Rx connection is required.
Plus
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.
Figure 37: IEEE C37.94 connection to compliant digital multiplexer
ELECTRICAL INSTALLATION
setting is "C37.94" or for
Protocol Encoding
Protocol
65