Wireless Sensor Networks are networks made up of tiny sensor nodes, in medium to large quantities, from several tens to hundreds and even thousands. They are used in fields ranging from military, medical, to structural health monitoring for buildings for example. We have introduced an instruction set simulator in our IDEA1 WSN design framework to account for a fine-grained representation of the software running on the node hardware. We modelled the communication between the nodes' microcontrollers and their radio interface and microcontroller and sensor, respectively. This was done at transaction level by use of the SystemC simulation kernel. An application was developed, consisting of eight nodes compressing this abstract and sending it to their coordinator.