For example, from 200 ns to 300 ns, the inputs With the integer data type, we are not directly involved in the bit-level definitions; however, it’s clear that the implementation will use a number of bits to represent the defined signals. Attributes of discrete or physical types and subtypes Table 4. See Attributes (user-defined) for details. Predefined attributes are in the Predefined Attributes section attribute identifier : type_mark ; attribute enum_encoding : string; -- user defined type my_state is (start, stop, ready, off, warmup); attribute enum_encoding of my_state : type is "001 010 011 100 111"; signal my_status : my_state := off; -- value "100" attribute specification As shown in Figure 2, “integer” has two predefined subtypes:The value integer’high represents the highest value of the integer. An attribute gives extra information about a specific part of a VHDL description. To clarify this, consider the following code:In principle, the intermediate calculations are performed employing the standard range of the integer type, i.e., 32 bits. Additionally, users can define new attributes. Similarly, the third and fourth declarations both need four bits.It’s important to note that while the simulator will check for the range of values assigned to an integer, this check occurs only when actually assigning a value, not during the intermediate calculations.

VHDL doesn’t specify the exact number of bits for the integer type, but any VHDL implementation should support at least a …

The most common type used in VHDL is the std_logic.Think of this type as a single bit, the digital information carried by a single physical wire.

An attribute gives extra information about a specific part of a VHDL description. The std_logic gives us a more fine-grained control over the resources in our design than the integer type, which we have been using in the previous tutorials.. Table 3. Normally, we want a wire in a digital interface to have either the value '1' or '0'. Attributes of the array type or objects of the array type true if index range of dimension n is ascending, false otherwise Implicit signal, equivalent to signal S, but delayed t units of time Implicit signal that has the value true when no event has occurred on S for t time units, false otherwise implicit signal that has the value true when no transaction has occurred on S for t time units, false otherwise implicit signal of type Bit whose value is changed in each simulation cycle in which a transaction occurs on S (signal S becomes active) true if an event has occurred on S in the current simulation cycle, false otherwise true if a transaction has occurred on S in the current simulation cycle, false otherwise the amount of time since last event occurred on S, if no event has yet occurred it returns Time'High the amount of time since last transaction occurred on S, if no event has yet occurred it returns Time'High the previous value of S before last event occurred on it true if the process is driving S or every element of a composite S, or false if the current value of the driver for S or any element of S in the process is determined by the null transaction the current value of the driver for S in the process containing the assignment statement to S a string representing the simple name, character literal or operator symbol defined in the declaration of the item E a string describing the path through the design hierarchy, from the root entity or package to the item E a string describing the path through the design hierarchy, from the root entity or package to the item E, but including the names of the entity and architecture bound to each component instance in the path Paths which can be written using E'Path_name and E'Instance_name are used for reporting and assertion statements.

However, since this won’t be an optimal implementation, the synthesis software will perform some optimizations according to the nature of the utilized operators. This article will discuss the VHDL integer data type.VHDL provides us with several options for the data type of the objects. In the VHDL standard a set of predefined attributes is defined. The integer data type and its subtypes are defined in the “standard” package from the “std” library. They allow specifying precisely where warnings or errors are generated. VHDL Compiler defines several kinds of attributes for VHDL object classes signal (port), component (cell), and entity (design).