In this paper we present a method that allows to observe and control the emulation of communicating systems consisting of hardware and software parts. The approach provides the ability to set breakpoints in either technology without breaking the protocol or loosing data. Systems may contain several software and hardware processes. Each process runs in a separate debugger while the presented approach provides the necessary synchronization between the processes that precludes loss of data at the communication interfaces due to breakpoints. Therefore it allows to continue the operation after a breakpoint which is essential for interactive debugging.