The NEMO floor control module

An electronic board, called floor control module (FCM), was developed for the NEMO project, an underwater neutrino telescope. The offshore FCM is in charge of providing interfaces toward instrumental control boards, collecting data from up to eight readout channels, packing and sending streams to the onshore laboratory through an optical fiber driven by a dense wavelength division multiplexing (DWDM) electro-optical transceiver. To obtain a common timing at each level of the apparatus, communication adopts the synchronous digital hierarchy (SDH) protocol, a standard telecommunication synchronous format which allows clock recovery from bitstream, thus simplifying the distribution network. The channel is fully bidirectional to allow underwater apparatus control. The same FCM, plugged into a PCI bus, can also be used onshore for data reception and transmission. This architecture provides a complete real-time data transport layer between the onshore laboratory and the underwater detector.