The VSC8166 demultiplexes a 2.488Gbp/s LVPECL serial input datastream (DI+) to 16-bit wide, LVPECL 155Mb/s parallel data outputs (D0:D15+) for SONET/SDH applications. It has an integrated clock and data recovery unit with an on-chip PLL that internally generates a 2.488GHz clock in phase with the incoming data. Internal divider circuits are used to take the high-speed clock and generate 155.52MHz (CLK16O+) and 77.76MHz (CLK32O+) LVPECL external output clocks. The incoming data is retimed and demultiplexed to a 16-bit word which is clocked out of the demultiplexer by the 155.52MHz output clock. Alarm functions support typical telecom system applications. A TTL Loss Of Lock (LOL) indicator can be externally enabled (LOLEN) to detect when the device goes out of lock, which would most often occur in the event of a loss of valid data. A TTL No-Reference (NOREF) output indicator flags when the LVPECL Clock Reference (REFCLK) input to the VSC8166 either is removed, or goes severely out of tolerance. For Loss Of Signal (LOS) conditions from an Optics Module, the VSC8166 provides a polarity (POL) input to accommodate any polarity differences. Only a single 3.3V power supply is required for device operation and the device is packaged in a thermally enhanced 128 Pin 14x20x2 mm PQFP Package.