The timing behavior of a real-time system depends not only on delays due to process synchronization, but also on resource requirements and scheduling. However, most real-time models have abstracted out resource-specific details, and thus assume operating environments such as maximum parallelism or pure interleaving. This paper presents a real-time formalism called Communicating Shared Resources (CSR). CSR consists of a programming language that allows the explicit expression of timing constraints and resources, and a computation model that resolves resource contention based on event priority. We provide a full denotational semantics for the programming language, grounded in our resource-based computation model. To illustrate CSR, we present a distributed robot system consisting of a robot arm and a sensor.