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Internal Interfaces• Uplink NRZI Modulation: The non-return-to-zero invert-ones (NRZI) modulatoris a flip-flop that toggles when the 4-to-5 bit is 1. This action attenuates thelow-frequency component of the 4-to-5 signal, making it suitable for passagethrough AC-coupled uplink circuitry. The maximum cable length between theSonar Head and the Sonar Processor is 200m. Care should be taken to ensurethat all cable and connectors in the uplink path are correctly terminatedand shielded. It is particularly important that a 75 ohm impedance be maintainedthroughout as even short impedance mis-matched lengths will causesignal degradation.• Downlink: The downlink from the Sonar Processor to the Sonar Head commandsthe transceiver circuits into various states and modes. The downlink isan RS232 type signal at 19200 baud, 8-bit, 1-stop bit, no parity. Nominal amplitudeis ±12V and packets are transmitted at irregular intervals. Thedownlink receiver is opto-isolated for protection. No more than 2ms data delayis tolerated by the transceiver.______________________________________________________________________SeaBat <strong>8101</strong> Operator's Manual 7-3 Version 3.02
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