Signals and Variables

Wyatt TD (2010) Pheromones and signature mixtures defining species-wide signals and variable cues for individuality in both invertebrates and vertebrates. J Comp Physiol A 196 685-700... 

Let V be aL finite set of processes indexed by an index set I, and let S and V be the sets of signals and variables in the program respectively. The cardinalities of the sets V, 5, and V are notated rip, ns, and ny, respectively. Variables, signals, boolean expressions, and statically determined time delays are denoted as v, s, e, and n respectively. Variables and signals in the elaborated VHDL program are renamed to vi and Si, where i is a positive index. Each line is assigned a label where i is the process index and j is the line index within the process (i, j are positive integers). 

A constant is a static object and so may be used in such a case. Also, integer and based literals (Chapter 6) and enumeration literals are static values. Signals and variables are dynamic objects. 

Determine which of the following logical signal and variable assignment operations are illegal. 

Examine the function of the If statement shown below. Construct the complete architecture for a VHDL description that performs the same function with a Case statement. Assume all signals and variables are of type BIT or BIT VECTOR. 

The same rules can be applied to arrays of signals and variables. In such a case, if one element of the array infers a storage element then so do all die elements. Level-sensitive latches are a special case discussed in section 5.4.4. 

When a design is simulated all signals and variables can be provided with initial values, avoiding any undefined states. Howevei this does not then guarantee that the circuit will function correctly when implemented in hardware, as each storage element will assume its own random state. Some mechanism must therefore be provided in the circuit to ensure that the storage elements are all correctly initialized or can be reset at any time to a known state. 

The shift register example has demonstrated how If and Wait statement templates can be used to infer sequential logic in a VHDL description. The format of these templates is reasonably fixed and signals and variables within the sequential logic must adhere to certain guidelines. In particular, the effect of creating incomplete If statements was demonstrated as one serious pitfall that should be avoided. 

Incomplete If statements can affect both signal and variable assignments. Consider the If statement ... 

Understanding the use of signals and variables within sequential logic blocks and where and when values are updated (section 5.42). 

Signals, variables and constants are at the heart of every design. They were introduced in Chapter 3. There are significant differences between these objects in terms of the way in which they can be used to hold and pass data. Chapter 5 demonstrated these differences with particular emphasis on signals and variables. 

The chemical shift of the hydroxyl proton signal is variable depending on solvent temperature and concentration Its precise position is not particularly significant m struc ture determination Because the signals due to hydroxyl protons are not usually split by other protons m the molecule and are often rather broad they are often fairly easy to... 

DOS and, concomitantly, on p [63-66], and, (iv) the temporal features of TOF signals, notably the universality of non-dispersive signals at variable sample length and electric field, and the transition to dispersive transport which, remarkably, does not bear out universality [67]. 

Finally we need to compare the variance of our estimator with the best attainable. It can be shown that The Cramer-Rao lower bound (CRLB) is a lower bound on the variance of an unbiased estimator (Kay, 1993). The quantities estimated can be fixed parameters with unknown values, random variables or a signal and essentially we are finding the best estimate we can possibly make. 

FIGURE 25.5 Sample constant amplitude signal (a) and variable amplitude signal (b). 

Figure 21.3 Modeling and simulation in the general context of the study of xenobiot-ics. The network of signals and regulatory pathways, sources of variability, and multistep regulation that are involved in this problem is shown together with its main components. It is important to realize how between-subject and between-event variation must be addressed in a model of the system that is not purely structural, but also statistical. The power of model-based data analysis is to elucidate the (main) subsystems and their putative role in overall regulation, at a variety of life stages, species, and functional (cell to organismal) levels. Images have been selected for illustrative purposes only. See color plate.

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