Process combinational/sequential logic

Domino reactions, which combine sequential transformations in a single pot, can allow the rapid development of complex products from simple starting materials. One design feature required for successful domino process involves control over the order of reaction events. Since Bronsted acids or Lewis acids are required for the initiation of nearly all azido-Schmidt reactions, combining such reactions with other acid-accelerated processes presents a logical starting point for assembling Schmidt-centric tandem reactions. 

This section has illustrated the important part that the Process statement plays in the design of sequential logic. In Chapter 4, its function in combinational design was also shown. It is good design practice to separate combinational and synchronous sections by using different processes. Box 5.1 offers some guidelines on how to use the process statement and illustrates its syntax. 

Bubble logic that implements universal Boolean logic in physical fluid dynamics has been demonstrated in [4]. A bubble traveling in a microchannel can represent a bit of information as well as carry a chemical payload. Therefore, it is possible to integrate chemistry with computation for process control. Since bubble logic preserves the information representation from input to output, devices can be cascaded to implement combinational and sequential Boolean logic. 

The Process statement part may only contain sequential statements such as If-Else, Case and For Loop (Chapter 6). These are executed in the order in which they appear and the behaviour will be modelled with combinational and/ or sequential (synchronous or asynchronous) logic. 

As this example has two clearly distinct sections, one combinational and one sequential, the hierarchy has been preserved and each process optimized independently. Again only area optimization has been attempted to remove simply the redundant or duplicated logic. Low, medium and high levels of effort were employed. 

This example may seem a little complicated, but it clearly demonstrates how a procedure can be used in both a sequential and concurrent manner. The concurrent procedure is effectively a process. This process may contain a Clock statement (but not a Walt statement Box 7.8) or may simply be a block of combinational logic, as in this case. As with any concurrent statement variables cannot be passed to the procedure but can be used inside it, as seen here. Refer again to Box 7.9 for more details. 

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