Black Box Short-Haul Modem-C Async (SHM-C Async), 4-Wire, StandaloneBlack Box Short Haul Modem C Async (SHM C Async), 4 Wire, Standalone The Black Box Short Haul Modem C Async (SHM C Async) is a compact, rugged solution designed to meet demanding data transmission needs across industrial environments. Whether youre deploying security systems, industrial automation networks, or simply linking remote workstations, this async modem delivers reliable, low latency communication over short distances. The SHM C Async