Time-triggered architectures (TTAs) are strong candidate platforms for safety-critical real-time applications. A typical time-triggered architecture is constituted by one or more clusters. Each cluster consists of nodes communicating with one another via a time-triggered communication protocol. Designing applications to run on such a platform is a challenging task. We address this problem by constructing a UML-based design framework which exposes the essential features of the time-triggered platforms at the UMLlevel and allows applications to be developed at a more abstract level before full implementation. To support preliminary functional validation, we have constructed a translator by which SystemC code can be automatically generated from UML designs. Our framework enables fast prototyping of time-triggered applications and early design validation. It also supports key design principles of TTAs, such as temporal firewalls and composability.