One major challenge in System-on-Chip (SoC) design is the definition and design of interfaces between hardware and software. Traditional ASIC designer and software designer model HW/SW interface twice. Using two separate models introduces a discontinuity between hardware and software. This paper introduces a unified HW/SW component model to describe t parts of HW/SW interface at different abstraction levels. The benefits of using the proposed model are two fold: first, it a single model to present system design from abstract specification to mixed HW/SW implementation and second, it full system simulation at different abstraction level during refinement flow. Categories and Subject Descriptors D.3.3 [Programming Languages]: Language Contructs and Features B.4.2 [Input/Output and Data Communications]: Input/Output Devices General Terms Algorithms, Design, Standardization, Languages Keywords Hardware/Software Interfaces, Hardware dependent Software, Embedded Systems