. High accurate external clock synchronization can only be achieved with adequate hardware support. We analyze the requirements yielding a specification and implementation of an ASIC running under the acronym UTCSU. It incorporates adder-based clocks to maintain both local time and accuracy, facilities to timestamp packets containing synchronization data, interfaces to couple GPS receivers, moderate application support, and self-test machinery. These novel clocks are distinguished by their fine grained rate adjustability and their hardware support for linear continuous amortization. Apart from addressing design and engineering issues of this chip, the paper provides a basic programming model as well. Keywords: Real-time systems, external clock synchronization, Universal Time Coordinated (UTC), adder-based clock (ABC), linear continuous amortization, accuracy intervals, Application Specific Integrated Circuit (ASIC), Very high speed integrated circuit Hardware Description Language (VHD...