STD Library (Standard Library)

STD Library (Standard Library)

It contains the following packages:

• standard = bit,boolean,integer,real, time
• textio = file operation, dosya işlemleri

It's a built-in library. So it is not necessary to reference it in VHDL designs.

Data Types Defined in STD Library (Pre-defined)

1. Bit
  It consists of 1 ve 0 elements.

Signal input:BIT;

"bit_vector" expression indicates that signal is an array of bits.

Signal output :BIT_VECTOR(6 downto 0);
Signal output :BIT_VECTOR(0 to 6);

2. Boolean

It consists of true and false values.

Signal sys_ready: boolean;

3. Integer 

It consists of positive and negative decimal values.

Signal level:intger; --32 bits 
Signal level :integer range 0 to 31; --5 bits

 4. Natural 

It consists of Integer values from 0 to 2³².

5. Positive 

It consists of Integer values from 1 to 2³²..

6. Character 

It consists of ASCII characters.

7. Time 

It consists of time types (ps=piko second, us:mikro second, ms=mili second, sec=seconds, min=minute, hr=hour)

Data Types Defined in IEEE.STD_LOGIC_1164 Package

1.STD_LOGIC type

It consists of nine elements explained below :

‘1’ : Logic 1
‘0’ : Logic 0
‘X’ : Bilinmeyen (unknown)
‘U’ : Uninitialized
‘Z’ : Tri-state (high empedans)
‘H’: Zayıf logic 1 (weak logic high)
‘L’ : Zayıf logic 0 (weak logic low)
‘W : Zayıf bilinmeyen (weak unknown)
‘-‘  : Önemsiz (don’t care)
Signal clk:std_logic;

"std_logic_vector" expression indicates that signal is an array of std_logic types.

Signal ready :std_logic_vector(3 downto 0);