The cognitive constraints of the human mind must drive the decisions in architecture and methodology design in order that the systems we build are comprehensible. This paper presents a methodology for the design of time-triggered embedded systems that leads to understandable artifacts. We lift the design process to a higher level of abstractionto the level of computational components that interact solely by the exchange of messages. The time-triggered architecture makes it possible to specify the temporal properties of component interfaces precisely and provides temporally predictable message communication, such that the precise behavior of a large design can be studied in the early phases of a design on the basis of the component interface specifications. This paper shows how the cognitive simplification strategies of abstraction, partitioning and segmentation are supported by the time-triggered architecture and its associated design methodology to construct evolvable embedded systems that can be readily understood and modified.