Port statement defined

The entity header can contain a generic statement. For synthesis, this defines constants that can be accessed by the port statement or the architecture body. A generic list (Chapter 5) is contained inside the generic statement, which has the syntax ... 

The top level of the proposed circuit was shown in Figure 7.1. The two blocks. Decoder and Enabler, have dear functions and well-defined I/O. The design process may therefore begin at this level. As a result, the top-level entity of the sequence follower contains a Port statement with data... 

In VHDL, a component declaration is required before instantiating a component. This defines the template of the component being instantiated and includes information such as, port mode or direction, port names and the data type of the ports. These templates or component declarations are bound to sub-design entities using configuration declaration statements. Hence, when reading in a VHDL netlist you... 

Workbench. That is, these structural components are not synthesized by the Workbench. However, they define the implicit ports (connections to a continuous assignment and instantiated submodules), and explicit ports (declared ports of the current module) between the behavior described in the always statement and these structural entities. 

Each identifier is the name of a port in the design. It is treated as a signal. The constraint, if any, applied to the type or subtype must be static. It may contain generics defined in a preceding generic statement. The default initial value expression of the port is ignored by the synthesizer. 

This occurs because the S3mthesizer does not see a JK flip flop in the process function but knows, from the clock condition in the Wait statement, that a sequential circuit is being inferred. As discussed in section 5.1.3, the choice of flip flop in an inferred sequential section is left entirely up to the synthesizer. It will therefore tend to select a simple one rather than a complex one, and so not risk the overspedfication of the circuit. Observe the feedback of S, which is required to determine the next state of the circuit. Because this signal is not only updated and output by the process but also read, the connection to the top level of the drcuit is defined in the schematic as bidirectional. This does not mean that it can be used as an input to the circuit as the entity declaration for this component states that the port Q, to which it is directly connected, is of mode output. 

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