![std lib vector code std lib vector code](https://i.stack.imgur.com/7YWxW.png)
The VHDL keyword “std_logic_vector” defines a vector of elements of type std_logic. For example, a_vec(2) will give the value of the rightmost element of the vector in Figure 4, which is val_2.įigure 4.
![std lib vector code std lib vector code](https://www.allaboutcircuits.com/uploads/articles/Arar_Std_Logic_Vector_2.jpg)
To access the value of an element from this vector, we can use the index numbers. For example, assume that, as shown in Figure 4, we use a vector of length three, a_vec, to represent three values: val_0, val_1, and val_2. To access an element of a vector, we need to define an index. To represent a group of signals, VHDL uses vector data types.
STD LIB VECTOR CODE CODE
This may seem like a simple idea, but we will see in a minute how this way of thinking makes the code more readable. What the circuit does is AND an element of a_vec with a corresponding element of b_vec. Similarly, the input ports b0, b1, and b2 can be grouped as another three-bit input port called b_vec. Let’s consider an alternative way of depicting the circuit in Figure 2.įigure 3 suggests that we can consider a0, a1, and a2 as a three-bit input port called, for example, a_vec. The drawback to the above code is that it presents each of the input/output ports as individual signals and doesn’t establish any relationship between them. The above code is correct however, we will see that it’s possible to have a more compact and readable VHDL description for this circuit. We can extend the previous code to obtain the VHDL description of Figure 2 as 1 library ieee ġ4 architecture Behavioral of circuit_2 is Now, assume that we need to write the VHDL code for the circuit in Figure 2. Here is the VHDL code for this circuit: 1 library ieee Ĩ architecture Behavioral of circuit_1 is Why Do We Need Vector Data Types?Ĭonsider the simple circuit in Figure 1, which was discussed in the previous article. Then, after reviewing some important features of the “std_logic_vector” data type, we will go over some coding styles that can help us avoid mistakes when utilizing vectors. We will first discuss the fact that vectors allow us to have a more compact and readable VHDL description, especially when dealing with large circuits. This article will review one of the most common data types in VHDL, i.e., the “std_logic_vector” data type. In a previous article on the VHDL hardware description language, we discussed the basic structure of VHDL code through several introductory examples. This article will review the "std_logic_vector" data type which is one of the most common data types in VHDL.