In MDE system-level approaches, the design of communication protocols and patterns is subject to the design of processing operations (computations) and to their mapping onto execution resources. However, this strategy allows to capture simple communication schemes (e.g., processor-bus-memory) and prevents to evaluate the performance of both computations and communications (e.g., impact of application traffic patterns onto the communication interconnect) in a single step. To solve these issues we introduce a novel design approach - the Ψ-chart - where we design communication patterns and protocols independently of a system’s functionality and resources, via dedicated models. At the mapping step, both application and communication models are bound to the platform resources and transformed to explore design alternatives for both computations and communications. We present the Ψ-chart and its implementation (i.e., communication models and Design Space Exploration) in TTool/DIPLODOCUS, a UML/SysML framework for the modeling, simulation, formal verification and automatic code generation of data-flow embedded systems. The effectiveness of our solution in terms of better design quality (e.g., portability, time) is demonstrated with the design of the physical layer of a ZigBee (IEEE 802.15.4) transmitter onto a multi-processor architecture.