Ieee C37.94 Interface - GE C70 Instruction Manual

CHAPTER 3: INSTALLATION
3.4.4.4 Receive timing
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 digital phase lock loop (DPLL) 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 serial communication controller (SCC) receive clock.

3.4.5 IEEE C37.94 interface

IEEE C37.94 is a standard interface between teleprotection equipment and digital multiplexers.
The UR-series IEEE C37.94 modules (module types 2I, 2J, 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. The
IEEE C37.94 standard defines a point-to-point optical link for synchronous data between a multiplexer and a teleprotection
device. Data speed 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) or 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 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 required
The UR-series C37.94 module can be connected directly to any compliant digital multiplexer that supports the IEEE C37.94
standard. The figure shows the concept.
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
Figure 3-48: Clock and data transitions
DIRECT INPUT AND OUTPUT COMMUNICATIONS
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