VHDL Tutorial

Bits type in VHDL
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Bits

 

Since VHDL is used to model digital systems, it is useful to have a data type to repre- sent bit values.  The predefined enumeration type bit serves this purpose.  It is defined

as

 

type bit is ('0', '1');

 

The logical operators that we mentioned for Boolean values can also be applied

to values of type bit, and they produce results of type bit The value 0 corresponds

to false, and 1 corresponds to true.   So, for example:

 

'0' and '1' = '0',    '1' xor '1' = '0'

 

The difference between the types boolean and bit is that boolean values are used

to  model  abstract  conditions,  whereas  bit  values  are  used  to  model  hardware  logic levels.   Thus, 0 represents a low logic level and 1 represents a high logic level.

 

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