VHDL Programming

102 Chapter Four Access types are very powerful tools for modeling complex and abstract types of systems. Access types bring pro ...

Data Types 103 WRITE(file, data)Procedure ENDFILE(file)Function, returns boolean Procedure READreads an object from the file a ...

104 Chapter Four disk where the file is located. (In most implementations this is true, but it is not necessarily true.) FILE TY ...

Data Types 105 Line 2 of the example declares a file type rom_data_file_tthat is used to declare a file object. In line 3, a rom ...

106 Chapter Four The type integer encompasses the minimum range -2,147,483,647 to 2,147,483,647. In the Standard package (a des ...

Data Types 107 USE WORK.mux_types.ALL; LIBRARY IEEE; USE IEEE.std_logic_1164.ALL; ENTITY mux8 IS PORT(I0, I1, I2, I3, I4, I5, PO ...

108 Chapter Four How variables are local to processes and subprograms and are used mainly as scratch pad areas for local calcul ...

Chapter 5 Subprograms and Packages In this chapter, subprograms and packages are discussed. Subprograms consist of procedures an ...

110 Chapter Five Subprograms Subprograms consist of procedures and functions. A procedure can return more than one argument; a f ...

Subprograms and Packages 111 IF S(i) = ‘ 1 ’ THEN --line 9 result := result + 1; --line 10 END IF; END LOOP; RETURN result; --li ...

112 Chapter Five available for use in the function. The exception to this statement are attributes‘STABLE,‘QUIET,‘TRANSACTION, a ...

Subprograms and Packages 113 created by port clkof entity dff. If there is a rising edge on the signal clk, then the dvalue is t ...

114 Chapter Five ‘ 0 ’—Logical 0 value ‘ 1 ’—Logical 1 value ‘Z’—High-impedance or open-collector value From the description ...

Subprograms and Packages 115 RETURN ‘Z’; END CASE; END convert4val; FUNCTION convert4value(S : fourvalue) RETURN fourval IS BEGI ...

116 Chapter Five directly to the component ports. A conversion function is needed to convert between the two value systems. If t ...

Subprograms and Packages 117 This method is much more verbose, requiring an intermediate temporary signal for each port of the c ...

118 Chapter Five RETURN Z; WHEN ZX => RETURN Z; WHEN R0 => RETURN L; WHEN R1 => RETURN H; WHEN RX => RETURN X; WHEN ...

Subprograms and Packages 119 The first component instantiation statement for the transcomponent labeled U1shows how conversion f ...

120 Chapter Five ZL HX Z L H X Z L H X L L X X H X H X X X X X Figure 5-1 Four State Truth Table. Let’s examine a resolution fun ...

Subprograms and Packages 121 Using all of this information, a designer can write a resolution function for this type. The resolu ...