Smart cards are one of the smallest computing platforms in use today. Due to their limited resources applications are often simple and less complex. High performance 32-bit smart cards, which were introduced by several vendors in the last years, allow the implementation of complex applications on smart cards. Additional to the high performance processor cores these smart cards contain coprocessors to reach the performance and power consumption goals. The interface between the processor and the coprocessor influences the performance and power consumption and should be evaluated early in the design process. We propose a hierarchical bus model for system-level smart card design which supports accurate energy dissipation estimation. The bus models have been implemented in SystemC 2.0 at transaction level layer one (cycle accurate) and layer two (timing estimation). We evaluate accuracy and simulation performance of the models and show their usage as bus functional models for a smart card application.