Clock expression, synchronous

ASYNC JFI illustrates an architecture with completely separate combinational and synchronous sections. Alternatively ASYNCJK shows how the synchronous section can hang off the combinational section. In this example, note that the clock expression is on the last branch of the If statement. It would be an error if this statement was followed by another Elsif or an Else statement. 

Circadian clocks are molecular time-keeping mechanisms found in a broad range of cell types from a variety of organisms. The primary roles of these clocks are to maintain their own 24 hour molecular rhythm and to drive the rhythmic expression of genes that control output processes in physiology, metabohsm and behaviour. Core features of the clock are its ability to synchronize to daily environmental speitgehers (e.g. hght—dark or temperature cycles), and then maintain rhythmic function when placed in constant conditions. 

Another problem with existing high-level description languages is that they usually have a built-in timing methodology that makes it difficult to express interfaces that include both synchronous and asynchronous behavior. These are quite common at the boundary between circuits, for example, when connecting two synchronous units that have different clocks or when connecting a synchronous device to an asynchronous communication bus. 

If the initialization signal, INTT, is high the normal shift operation occurs. The register will be initialized if INIT goes low. These operations inside a process are synchronous when a Wait statement is used with the dock expression. The trigger in this case is a rising clock edge. See Box 5.7 for more details on this construct. 

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